Blood donor screening: Medical history and deferral criteria

INTRODUCTION — 

Blood transfusion is a life-saving therapy that is critical to the management of diverse conditions. It relies on a safe and sufficient blood supply that in turn relies on blood donors.

The purpose of blood donor screening is twofold:

●To identify any medical and/or behavioral risk factors that could pose a risk to the transfusion recipient.

●To identify any factors that could render the donation process unsafe for the prospective donor.

Blood donor screening includes the following components, with deferral of donors at increased risk, either indefinitely or until the risk is considered to be mitigated:

●Donor history

●Limited physical examination (vital signs, examination of the skin where the needle will be placed)

●Laboratory-based testing

This topic reviews the blood donor medical history and associated deferral criteria. Separate topics discuss:

●Donor physical examination – (See "Blood donor screening: Overview of recipient and donor protections", section on 'Vital signs'.)

●Laboratory testing of donated blood – (See "Blood donor screening: Laboratory testing".)

●Other donor and recipient protections – (See "Blood donor screening: Overview of recipient and donor protections".)

OVERVIEW — 

Effective donor screening protects both donors and prospective transfusion recipients from risk. It also avoids the costs and burdens of collecting blood that will otherwise be subsequently discarded due to infectious risk.

The donor evaluation includes a medical history questionnaire and a limited physical examination (vital signs including blood pressure and temperature check; skin check). The examination is discussed separately. (See "Blood donor screening: Overview of recipient and donor protections", section on 'Screening at the donation site' and "Blood donor screening: Overview of recipient and donor protections", section on 'General procedures to protect the donor'.)

Age cutoff — The minimal age for donation is legally established by individual states in the United States and is either 16 or 17 years; donors who are legally minors need written consent of a parent or guardian. (See "Blood donor screening: Overview of recipient and donor protections", section on 'Age and weight cutoffs'.)

Most blood centers do not have an upper age limit for donation; this policy is based on studies documenting that individuals over the age of 65 who met all other donation criteria had no greater frequency of severe or life-threatening reactions and had lower rates of post-transfusion reactions than younger donors [1].

Role and key components of the medical history — The donor history questionnaire is administered to determine whether the prospective donor is eligible to give blood or is deferred from donating on that day (and possibly in the future). Questions are continually reviewed and updated as new risks arise.

The medical history includes basic information about risk factors for transfusion-transmitted infections and donor medical conditions. A combination of educational materials and specific questions is intended to help donors provide the most accurate and complete medical history.

Donor history questions relevant to safety address the following:

●Pathogens for which laboratory testing is also done (eg, human immunodeficiency virus [HIV], hepatitis B virus [HBV], hepatitis C virus [HCV], and syphilis). (See "Blood donor screening: Laboratory testing", section on 'Infectious disease screening and surveillance'.)

●Pathogens for which laboratory testing is not done, such as certain parasitic and prion disease agents. (See 'Parasites' below and 'Prions (Creutzfeldt-Jakob disease, variant CJD)' below and 'Neurodegenerative and other neurologic disorders' below.)

●Medications taken by the donor which have teratogenic potential for the recipient. (See 'Potential teratogens' below.)

●History of cancer in the donor. (See 'History of cancer' below.)

●Medical conditions that pose a risk to the prospective donor, such as heart disease, lung disease, or a bleeding disorder. (See 'Other medical conditions' below.)

All prospective blood donors are required to answer all medical history questions.

The donor history is not used to distinguish different units of blood for different purposes, with the exception of certain characteristics that are only relevant for plasma. (See "Transfusion-related acute lung injury (TRALI)", section on 'Mitigating TRALI risk from plasma via deferral of multiparous female donors'.)

Recipients do not have the option to select specific donor characteristics such as age, sex, sexual orientation, or vaccination status [2]. Large studies in transfusion recipients report no difference in multiple outcomes based on the inferred or documented coronavirus disease 2019 (COVID-19) vaccination status of the donor [3,4].

Duration of deferrals — Deferral, if required, may either be temporary (for a defined time interval, usually 3 or 12 months), indefinite, or permanent, as listed in the table (table 1). Due to ongoing improvements in testing methods over the years and anticipated improvements in the future, most long-term deferrals are indefinite rather than permanent.

●Temporary – Deferrals for a defined time interval are used to exclude individuals with temporary risk factors for infectious or medication-related complications.

Examples include travel or residence in a malaria-endemic region of the world, receipt of a tattoo, recreational injection drug use, or blood transfusion. (See 'Malaria' below and 'Body piercings, tattoos, injection drug use, and recent transfusion' below.)

For all time-related deferrals, the deferral starts from the last date of exposure.

●Indefinite – Indefinite deferral is for an unspecified period of time. It does not have a time limit and is permanent unless donor eligibility criteria or methods to eliminate false-positive laboratory results are changed in the future.

Examples include a previous deferral (put into place during the early years of the HIV epidemic) for men who have sex with men; this was subsequently revised to a temporary deferral focusing on high-risk behaviors for both male and female donors. (See 'HIV' below.)

●Permanent – Permanent deferral means the donor can never donate again. It is used for conditions for which risk and associated deferral criteria will not change.

Examples include confirmed HIV laboratory test results, HBV test results of repeatedly reactive/confirmed hepatitis B surface antigen (HBsAg) positive and with detectable antibodies to hepatitis B core antigen (anti-HBc), and certain prion disorder diagnoses. (See 'HIV' below and 'Hepatitis B and C viruses' below and 'Prions (Creutzfeldt-Jakob disease, variant CJD)' below.)

Additional resources listing deferrals are provided by the Association for the Advancement of Blood & Biotherapies (AABB) [5,6].

How to administer the donor history questionnaire — In the United States, the medical history questionnaire must contain questions to identify risk factors for pathogens that have been designated by the US Food and Drug Administration (FDA) as relevant for transfusion-transmissible infectious diseases. For those pathogens, the FDA has established criteria for eligibility to donate as well as for donor deferral. In other countries, questions are dictated by the appropriate regulatory authority [7,8].

In the United States, variation is permitted in the exact wording of questions or in the format of interviewing blood donors. Each blood collection center's medical history standard operating procedure (SOP) must be approved by the FDA. The FDA maintains an online list of its guidances for industry related to blood collection, blood processing, and blood transfusion (blood guidances) [9].

Further, in the United States, an interagency task force under the auspices of the Association for the Advancement of Blood & Biotherapies (AABB) developed and standardized a uniform set of donor questions (table 2) and validated these through cognitively-based research protocols [7,10].

This initial Uniform Donor History Questionnaire (UDHQ) and its subsequent revisions (up to version 4.0) have been approved by the FDA and, though not required, are used by most blood centers [6,11,12]. The UDHQ can be administered verbally or can be self-administered, with follow-up questioning by a health historian if the donor's responses raise questions about donor eligibility.

●Verbal history – The value of donor history questions depends on the willingness of potential donors to provide accurate information about their behaviors, general health, risk factors for infectious diseases, and medications.

To optimize the likelihood of accurate responses, staff at the donation site should be encouraged to use appropriate nonjudgmental language, avoid culturally stigmatized terms, and refrain from behaviors that may be perceived as pressuring or judging the donor.

●Computer-assisted – Many blood centers have implemented a computer-assisted self-interviewing (CASI) process that includes audio, pictorial (visual), and touch-screen components. A two-year evaluation at one blood center showed that identification of high-risk behaviors among prospective first-time donors significantly increased following the use of CASI when compared with results obtained from the previously administered verbal questionnaire [13].

●At the donation center or before arrival – Historically, the questionnaire had to be administered on the day of donation at the blood donation facility. Some blood centers have moved to providing the option of answering medical history questions through an online portal on the day of donation, prior to the donor arriving at the blood collection facility.

●Abbreviated questionnaire – Because many questions in the medical history refer to events in the remote past, the FDA also approved an abbreviated donor history questionnaire (aDHQ) designed to identify recent changes in medical, behavioral, and travel information that have occurred since a donor's previous donation [12].

The aDHQ eliminates questions about events or behaviors that, if a donor had previously answered "no" on the UDHQ, would not need to be asked in future interviews of that donor. To be eligible to receive the aDHQ, the donor has to donate at an acceptable frequency, and the blood collection agency needs to have a policy permitting use of this instrument.

Evidence for accuracy of donor responses — The accuracy of donor responses to medical history questionnaires has been evaluated in the following studies:

●General donor pool – Two retrospective studies from the Retrovirus Epidemiology Donor Study (REDS) published in 1993 and 1998 used anonymous post-donation surveys mailed to individuals who had donated blood within the previous four to eight weeks (together totaling approximately 100,000 donors) and compared results with information provided at the time of donation [14,15]. Among respondents, approximately 2 to 3 percent reported behaviors that would have resulted in deferral had they been disclosed at the time of donation. A REDS post-donation survey study conducted in 2013 (at a time when men who have sex with men [MSM] sexual activity required an indefinite deferral from donation) reported that 2.6 percent of male blood donors admitted to MSM sexual activity that they had not reported at the time of donation [16].

●HIV and hepatitis seropositive donors – Interview studies have documented that individuals who are seropositive for HIV or hepatitis viruses do not always disclose their risk factors at the time of donation, nor do they use the post-donation confidential call-back mechanism to disclose these risk factors [17-19]. Reasons for proceeding with the donation include not reading or fully comprehending the information in the donation material, feeling pressure to donate, desiring to be tested for HIV or hepatitis viruses, and the impression that laboratory screening would identify infected blood and lead to its removal. Some individuals did not consider certain behaviors to be high risk because they were infrequent, were not recent, or had subsequently been modified.

These and other studies illustrate that a low level of increased risk continues to occur for certain transfusion-transmitted infections and that this risk is not identified by donor questioning. Continued efforts to improve the sensitivity of behavioral screening appear to be warranted [20]; laboratory testing and the potential for pathogen-reduction technologies remain critical. (See "Blood donor screening: Laboratory testing" and "Pathogen inactivation of blood products", section on 'Available products'.)

GENERAL INFECTIOUS DISEASE SCREENING QUESTIONS

Symptoms of active infection — Blood is not collected from persons who are febrile at the time of donation or who state that they do not feel well [5]. (See 'Recent incarceration, vaccination, antibiotics, or antiviral medications' below.)

This deferral is designed to exclude donors who may be bacteremic and to prevent transmission of bacterial infection from donor to recipient. (See "Transfusion-transmitted bacterial infection".)

These requirements are also applied to candidates for autologous donation, since cases of transfusion-induced sepsis have occurred in recipients of autologous blood [21]. (See "Surgical blood conservation: Preoperative autologous blood donation".)

Questions about symptoms such as fever or feeling unwell also can help exclude donors who might transmit other infectious organisms. (See 'Viruses' below and 'Bacteria' below and 'Parasites' below and 'Prions (Creutzfeldt-Jakob disease, variant CJD)' below.)

Recent incarceration, vaccination, antibiotics, or antiviral medications — Donors are asked about any vaccinations, antibiotic use, or any other medications taken to treat infections.

●Incarceration – Donors are asked if, in the last 12 months, they have been in juvenile detention, lockup, jail, or prison for 72 hours or more consecutively; if so, they are deferred for 12 months since the date of last occurrence.

●Vaccination – Deferral periods following vaccination vary based on the type of vaccine (table 1).

There is no deferral period for donors who are asymptomatic after receiving toxoids, synthetic vaccines, or killed vaccines, including COVID-19 vaccines [22,23]. The deferral period for live or attenuated vaccines ranges from no deferral for some vaccines such as pertussis or tetanus, to four weeks for others such as rubella, depending on the vaccine type and targeted pathogen.

Vaccination with live or attenuated viruses has the theoretical risk of transmitting infection. In some cases, transfusion-related transmission of a virus from a live virus vaccine has been reported, such as transfusion-related transmission of yellow fever virus from donors with recent yellow fever vaccination in whom an accurate vaccination history was not obtained [24].

•COVID-19 – Individuals who have been vaccinated for COVID-19 can donate blood or blood components. Those who have received a messenger ribonucleic acid (mRNA) vaccine or other non-infectious vaccine (nonreplicating, inactivated) can donate immediately. The Association for the Advancement of Blood & Biotherapies (AABB) has created a one-page fact sheet to explain the safety of transfusions from individuals who have been vaccinated [25].

Donation of COVID-19 convalescent plasma is discussed separately. (See "COVID-19: Convalescent plasma and hyperimmune globulin", section on 'Plasma donation'.)

•Smallpox – When the possibility arose that individuals in the United States population might receive smallpox vaccination using a live virus vaccine, specific questions were added to the donor history to address recent vaccination and skin contact with someone who was recently vaccinated. Positive responses required temporary deferrals (minimum of three weeks) to ensure the potential donor was beyond the period of viremia [26]. Although smallpox vaccination campaigns are not ongoing, this question remains on the Uniform Donor History Questionnaire (UDHQ) (table 2).

•Experimental, unlicensed vaccines – The deferral period may be as long as 12 months but may be shorter at the discretion of the facility's medical director. Deferral intervals may vary between different blood collection organizations [22].

●Antibiotics – Donors who are taking a systemic antibiotic for infection are deferred until they complete their full course of treatment. This requirement is designed to prevent transmission of bacteria for which the antibiotic was prescribed and thereby prevent resultant sepsis in the recipient.

Donors who are taking antibiotics for acne treatment are not deferred.

●Antiretroviral therapy (ART) or preexposure prophylaxis (PrEP) for HIV – Questions about HIV ART, PrEP, and postexposure prophylaxis (PEP) were added to the donor history questions after it was found that some individuals on a PrEP regimen or ART therapy were donating blood, despite the fact that medical history questions about HIV risk should have been cause for deferral [27].

ART is active therapy for HIV infection. Individuals who are currently or who have ever in the past received ART for confirmed HIV infection are permanently deferred [22].

HIV PrEP and PEP are preventive therapies for individuals without HIV; use of HIV PrEP has expanded dramatically.

•Individuals on a regimen of PrEP or PEP with tenofovir (Truvada), emtricitabine (Descovy), dolutegravir (Tivicay), or raltegravir (Isentress) are deferred until they have been off of their regimen for three months [22].

•For the longer-acting injectable PrEP medication cabotegravir (Apretude), the deferral is two years [22]; this is due to a much longer half-life of the drug in the circulation [28,29].

The rationale for these deferral periods is that these medications may suppress HIV to levels that are below the limit of detection of HIV laboratory tests but that are still high enough to result in transfusion transmission [27].

Other non-HIV antiviral medications are not included in the UDHQ. Many of these were not available when the questions were developed, and it is likely that donors taking other antiviral medications would most likely answer that they do not feel well or are taking a medication for infection. (See 'Symptoms of active infection' above.)

Other medications that may result in deferral are discussed below. (See 'Medications taken by the donor' below.)

Body piercings, tattoos, injection drug use, and recent transfusion — Questions about receiving a tattoo or body piercing within the last three months (previously the interval was the last 12 months) are asked due to concerns about HIV, hepatitis, or other infectious disease transmission [30]. However, affirmative answers do not necessarily result in deferral:

●Piercings – Most blood centers will accept donors with body piercing(s), provided the procedure was performed with sterile, single-use equipment (table 1).

●Tattoos – Donors with tattoos or permanent makeup are deferred for three months (previously 12 months) after the exposure, unless the application was done using sterile needles and nonreusable ink in a state that has a regulatory body that licenses tattoo parlors. If these conditions are met, and at the discretion of the local blood collection agency, donor deferral is not necessary.

●Injection drug use – Donors who have used a recreational nonprescription injection drug are deferred for three months since the exposure.

●Transfusions – Persons who have received a blood transfusion are deferred for three months since the transfusion (previously was 12 months).

Xenotransplantation and other exposures — Donors who have ever received a xenotransplant (tissue or organ from another animal species) are permanently deferred, with exceptions of porcine heart valves or porcine insulin.

The rationale is to avoid zoonotic infections.

SCREENING QUESTIONS ABOUT SPECIFIC PATHOGENS — 

For some infectious pathogens, screening includes donor history questions and laboratory testing. For others, screening relies on donor history questions alone or laboratory testing alone, but not both.

The following sections describe organisms for which donor history is routinely assessed. Laboratory testing is discussed separately. (See "Blood donor screening: Laboratory testing".)

Organisms for which a donor history is not taken, along with the rationale, are discussed below. (See 'Past responses to emerging infectious diseases and their impact on donor screening' below.)

Viruses — The table lists risks of transfusion-transmitted viral infections (table 3). These risks and questions to elicit them are discussed in the following sections.

HIV — HIV (human immunodeficiency virus) screening involves donor history questions and laboratory testing. (See "Blood donor screening: Laboratory testing", section on 'HIV-1 and HIV-2'.)

●Risk – The risk of HIV from blood transfusion in high-resource countries is estimated to be approximately 1 in 1.6 to 2.3 million units, when blood is tested using nucleic acid testing (NAT) for viral RNA (table 3). This risk estimate is significantly lower compared with the early years of the HIV epidemic in the 1980s [31,32].

●Reasons for reduced risk – The following account for reductions in risk:

•Reduced prevalence in the blood donor population – The rate of HIV seropositivity has declined in the United States blood donor population (individuals who have passed the screening and donate blood) from approximately 3.5 per 10,000 donations in the late 1980s to approximately 0.3 per 10,000 donations in the 2010s [33,34]. (See "Global epidemiology of HIV infection", section on 'Worldwide statistics'.)

•Identification of risk factors and education about donor deferral – Donor medical history screening educates donors about risk factors and facilitates deferral, including self-deferral, at various times before and after donation.

•Laboratory testing – (See "Blood donor screening: Laboratory testing", section on 'HIV-1 and HIV-2'.)

•For plasma derivatives, additional purification and processing steps – The risk of HIV transmission from the following is zero or negligible.

-IVIG, SCIG, albumin – HIV is inactivated by the purification process used to produce albumin and immune globulin products (intravenous immune globulin [IVIG] and subcutaneous immune globulin [SCIG]). There has never been a documented case of HIV transmission from albumin or immune globulin preparations. (See "Intravenous plasma derivatives and recombinant DNA-produced coagulation factors".)

-Plasma-derived clotting factors – Prior to 1984, many people with hemophilia who received plasma-derived clotting factor concentrates developed HIV [35]. Improved viral inactivation procedures (pasteurization, chromatography, solvent/detergent treatment) for plasma derivatives were added in the mid-1980s, and since then, there have been no documented HIV transmissions from clotting factor concentrates. In vitro data demonstrate that these procedures kill HIV in a logarithmic fashion [36]. Testing of donors is still required to exclude plasma with extremely high viral titers that might otherwise escape these inactivation procedures.

•Pathogen inactivation – Some blood products are treated with pathogen inactivation procedures that damage nucleic acids, destroying HIV and other pathogens. (See "Pathogen inactivation of blood products", section on 'Available products'.)

●Reasons for exceedingly rare transmission – Remaining reasons for HIV transmission include [37]:

•Brief period of negative laboratory testing after infection – Despite medical history and laboratory testing, there remains an exceedingly rare possibility for HIV transmission if blood is donated during the period when the donor is infectious but laboratory testing is negative [18,31,33,38]. This period is approximately 8 to 11 days depending on the type of nucleic acid testing used (individual donors versus minipools of donors). (See "Blood donor screening: Laboratory testing", section on 'HIV-1 and HIV-2'.)

Infection may occur with as few as two to three HIV virions in the entire plasma volume of the transfused blood component [31,39,40]. Transfusion-transmission risk is proportional to the volume of plasma in the transfused blood component; as an example, to transmit infection, a red blood cell (RBC) component that contains approximately 20 mL of plasma will require a 10-fold greater concentration of virions in the donor's blood than will a plasma component (a unit of Fresh Frozen Plasma [FFP] contains approximately 200 mL of plasma).

•HIV genetic variation – In principle, available laboratory testing may fail to identify genetic variants of HIV that evolve over time, although this has never been documented.

HIV testing includes serologic (antibody) assays for HIV-1, the overwhelmingly predominant strain responsible for transfusion-transmitted HIV prior to laboratory testing, and HIV-2, which was implicated in fewer than 50 cases of transfusion-transmitted HIV, occurring primarily in Portugal [41].

Antibodies to HIV-1 and HIV-2 show extensive crossreactivity; as a result, up to 90 percent of sera from HIV-2-infected persons test positive on US Food and Drug Administration (FDA)-licensed HIV-1-based screening assays [42]. There have been no cases of HIV-2 transmission after HIV-1 and HIV-2 serologic testing were instituted in Europe and North America.

•Clerical error – Using two independent methods of testing (HIV-1 and HIV-2 antibody and HIV-1 RNA) on each unit greatly decreases the risk of infection caused by clerical error. (See "Blood donor screening: Laboratory testing", section on 'HIV-1 and HIV-2'.)

●Donor education and donor history questions – Donors are given educational materials to read at the time of donation. During the donor interview, prospective donors are asked questions related to their HIV status, HIV treatment or prophylaxis, and behaviors associated with increased risk for HIV infection (table 1) [43].

The educational material also describes symptoms that are potentially consistent with acute HIV infection (fever, enlarged lymph nodes, sore throat, rash) [43]. Donors must sign an acknowledgment agreeing not to donate if the donor is aware of a potential risk to recipients, including risk of HIV infection.

HIV-related questions (and associated deferral criteria) have evolved over time from focusing on specific groups of individuals (men who have sex with men) to focusing on individual high-risk behaviors (high-risk sexual activity, commercial sex work, injection drug use, history of sexually transmitted diseases, use of antiretroviral therapy [ART]) [44].

In 2023, the FDA gave approval for a screening process known as individualized risk assessment, in which all donors are asked the same sexual risk-based questions regardless of their sex or gender identity [44,45]. This individualized risk assessment has been adopted throughout the United States blood collection system.

Donors are asked if they have had a new sexual partner or >1 sexual partner in the past three months, and if they answer positively, they are asked about anal sex (table 2). Additional questions are about sex in exchange for money and sex with a person who has ever had HIV.

●Deferral criteria – Donors who report that they have ever been diagnosed with or treated for HIV are permanently deferred.

Donors who have had anal sex with a new partner or anal sex and more than one partner in the past three months as well as other high-risk behaviors are deferred for three months since the exposure (table 1).

This 2023 policy change is informed by data from a multicenter, multiyear study in the United States [46]. It closely parallels policies previously instituted in the United Kingdom and Canada [47,48]. It also reflects the reduced window period with modern laboratory testing. (See "Blood donor screening: Laboratory testing", section on 'HIV-1 and HIV-2'.)

The 2023 FDA recommendations revised their previous 12-month deferral to include a three-month deferral for individuals who report any of the following [44]:

•A new sexual partner or >1 sexual partner in the past three months and anal sex in the past three months.

•Sex in exchange for money or drugs or sex with a commercial sex worker.

•Sex with a person who has ever had HIV or tested positive for HIV.

•Exposure to blood through needlestick injury or blood splash to mucous membrane or non-intact skin.

•Intravenous recreational drugs or sex with a person who used intravenous recreational drugs in the prior three months.

•Diagnosis or treatment for a sexually transmitted disease (syphilis or gonorrhea).

•Oral preexposure prophylaxis (PrEP) or postexposure prophylaxis (PEP) for HIV.

•Body piercing or tattoo (unless done in an appropriately certified venue with sterile equipment).

•Transfusion of whole blood or a blood component.

Deferral for the use of PrEP and PEP applies regardless of whether there are HIV risk factors or an HIV exposure. If PrEP or PEP is used in injectable form, the deferral is two years rather than three months. Individuals should not stop taking PrEP or PEP in order to donate blood [44]. (See 'Recent incarceration, vaccination, antibiotics, or antiviral medications' above.)

Additional details about body piercings and tattoos are discussed above. (See 'Body piercings, tattoos, injection drug use, and recent transfusion' above.)

Hepatitis B and C viruses — Hepatitis screening is primarily done by laboratory testing for hepatitis B virus (HBV) and hepatitis C virus (HCV). Hepatitis A virus is not transfusion-transmitted. (See "Blood donor screening: Laboratory testing", section on 'Hepatitis B virus' and "Blood donor screening: Laboratory testing", section on 'Hepatitis C virus'.)

United States federal guidelines for preventing transfusion-transmitted hepatitis were established decades ago in the Code of Federal Regulations and subsequently revised [49].

As of 2016, there is no longer an FDA or Association for the Advancement of Blood & Biotherapies (AABB) requirement to ask the donor about a history of viral hepatitis [49]. However, if a potential donor volunteers a history of a prior diagnosis of hepatitis B virus (HBV) infection, hepatitis C virus (HCV) infection (even if treated and cured), or viral hepatitis of unknown type, the donor is permanently deferred.

Additional deferral policies are as follows:

●Persons reporting current or previously confirmed positivity for hepatitis B surface antigen (HBsAg) are permanently deferred. Persons who volunteer a history of prior diagnosis of HBV infection are also permanently deferred.

●Persons who have received hepatitis B immune globulin (HBIG) are deferred for one year. (See 'Recent incarceration, vaccination, antibiotics, or antiviral medications' above.)

●Persons with a history of close contact with someone who has viral hepatitis are deferred for three months following their last potential exposure.

This applies to close contact with persons who have HBV, symptomatic HCV, or viral hepatitis of unknown origin.

The definition of close contact with a person with viral hepatitis includes sexual contact. Other aspects of close contact are more challenging to define. The definition suggested by the AABB as part of its Uniform Donor History Questionnaire materials is living in the same dwelling; this implies the sharing of household, kitchen, or toilet facilities. For HBV, this definition appears reasonable, since HBV can rarely be transmitted from an acutely infected patient to a household contact, probably through nonsexual contact with body fluids [50]. Data do not support similar transmission for HCV, and deferral is not required for sexual or other close contact with an asymptomatic HCV carrier [51].

Individuals should not donate blood as a way to get tested for HBV or HCV. Testing and vaccination are discussed separately. (See "Hepatitis B virus: Screening and diagnosis in adults" and "Screening and diagnosis of chronic hepatitis C virus infection" and "Hepatitis B virus immunization in adults".)

Hepatitis E virus (HEV) — Details of virology, transmission, and clinical features of HEV are discussed separately. (See "Hepatitis E virus infection".)

There are no donor questions regarding HEV, but HEV is a transfusion-transmitted infection, and several countries conduct routine laboratory testing of donated blood for HEV. (See "Blood donor screening: Laboratory testing", section on 'Overview of laboratory testing'.)

West Nile virus (WNV) — WNV is a mosquito-borne flavivirus that can cause encephalitis. Most transmission is via mosquitoes. (See "Epidemiology and pathogenesis of West Nile virus infection" and "Clinical manifestations and diagnosis of West Nile virus infection".)

WNV screening is done by laboratory testing, which has been in place since 2003. (See "Blood donor screening: Laboratory testing", section on 'West Nile virus'.)

A donor history question related to WNV (fever plus headache during the week prior to donation) was included for a period of time based on transfusion-transmitted infections that occurred before WNV laboratory testing was implemented. The question was subsequently removed after an evaluation failed to find a correlation between these symptoms and WNV infection [52,53]. As with other acute viral syndromes, a general donor history question about whether the donor feels well may elicit nonspecific systemic complaints leading to donor deferral. (See 'Symptoms of active infection' above.)

Individuals identified to have WNV based on laboratory testing are temporarily deferred for 120 days [53].

HTLV — Two closely related retroviruses, human T cell lymphotropic viruses (HTLV)-I and HTLV-II, are transmissible by blood transfusion. HTLV-I can cause adult T cell leukemia-lymphoma; both HTLV-I and HTLV-II rarely cause HTLV-associated myelopathy (HAM). (See "Human T-lymphotropic virus type I: Virology, pathogenesis, and epidemiology" and "Human T-lymphotropic virus type I: Disease associations, diagnosis, and treatment".)

Most carriers of either of these HTLV viruses are asymptomatic. There is no donor screening question specifically targeted to HTLV-at-risk donors; however, the question on injection drug use will identify some HTLV-II-infected donors, since this is a major route of spread of this virus in the United States. (See 'Body piercings, tattoos, injection drug use, and recent transfusion' above.)

Each unit of blood is screened in a single assay that detects antibodies to both of these viruses. (See "Blood donor screening: Laboratory testing", section on 'HTLV-I and HTLV-II'.)

Dengue virus — Dengue viruses are transmitted by mosquitoes. Infection may be asymptomatic or present with a broad range of clinical manifestations including a mild febrile illness to a life-threatening shock syndrome. (See "Dengue virus infection: Pathogenesis" and "Dengue virus infection: Prevention and treatment" and "Dengue virus infection: Clinical manifestations and diagnosis".)

Although Dengue has been reported to be transfusion transmissible, the risk in the United States is very low, and donors are not routinely screened in the United States by history or laboratory testing.

Bacteria

●Syphilis – There is one donor history question that inquires about a history of having had or having been treated for syphilis or gonorrhea in the past three months. A positive answer results in a three-month deferral from the time the treatment was completed. The presumed rationale for this question was to detect donor behaviors that put a donor at risk for transfusion transmission of other infectious agents; however, accumulated data suggest this rationale may no longer apply, as discussed separately. (See "Blood donor screening: Laboratory testing", section on 'Syphilis'.)

Syphilis can be transfusion transmitted; gonorrhea cannot. Each donated unit undergoes laboratory testing for the causative bacteria for syphilis, Treponema pallidum. (See "Blood donor screening: Laboratory testing", section on 'Syphilis'.)

●Other bacteria – No other bacteria exposures are specifically queried, but questions about symptoms of active infection and recent antibiotics are used. (See 'Symptoms of active infection' above and 'Recent incarceration, vaccination, antibiotics, or antiviral medications' above.)

Mitigation measures to decrease the risk of transfusion-transmitted bacterial infection are discussed separately. These include examination of the skin, cleaning of the skin site, and the availability of a phone number for post-donation call back. (See "Transfusion-transmitted bacterial infection", section on 'Platelet-specific guidance and requirements' and "Blood donor screening: Overview of recipient and donor protections", section on 'Protection of the recipient' and "Pathogen inactivation of blood products".)

Parasites

Malaria — Malaria is screened by donor history questions. Laboratory testing is not done in the United States but is under discussion. (See "Blood donor screening: Laboratory testing", section on 'Other transfusion-transmitted infections'.)

●Risk – Several Plasmodium species can cause malaria; these are mosquito-borne protozoal RBC parasites. (See "Malaria: Clinical manifestations and diagnosis in nonpregnant adults and children" and "Non-falciparum malaria: P. vivax, P. ovale, and P. malariae" and "Non-falciparum malaria: Plasmodium knowlesi".)

Transfusion-transmitted malaria (TTM) is common in regions of the world where malaria is endemic. The main risk is with RBC and whole blood units.

Approaches to reduce the risk of TTM differ between endemic and non-endemic countries.

●Endemic regions, donor screening – TTM poses a complex challenge for endemic regions, which are disproportionately low and low-middle income countries that lack resources for laboratory testing of donors for malaria. Additional considerations include the high rates of deferral that would occur if sensitive laboratory testing were performed, the high numbers of donors with a history of malaria, and lack of donors to meet the transfusion demand [54-56].

General assessment of well-being through questioning and limited physical examination may defer those with active infection. (See 'Symptoms of active infection' above.)

However, chronic, asymptomatic parasitemia is well described and can still confer risk of TTM. Some blood centers in endemic countries examine donor peripheral blood smears microscopically to identify infected donors, although this is a labor-intensive and relatively insensitive approach.

●Non-endemic regions, donor history questions – Donors are asked whether they have ever had malaria or if they have traveled outside the United States or Canada in the past three years (table 2) [57].

●Deferral criteria – Criteria differ based on the duration of the exposure (table 1).

•Residence or infection – Individuals who have resided in a malaria-endemic country (continuous stay for >5 years) or who have recovered from malaria are deferred for three years after departure (assuming they do not travel to a malaria-endemic country during that period) or after becoming asymptomatic, respectively [57]. This criterion is based upon the premise that such individuals may have partial tolerance to malarial parasites, thereby resulting in the absence of or delay of malarial symptoms.

Active infection may also be identified by general questions about fever and general well-being, limited physical examination, and hemoglobin. (See 'Symptoms of active infection' above and "Blood donor screening: Overview of recipient and donor protections".)

•Travel – Individuals who have traveled to a malaria-endemic region for 24 hours or more are deferred for three months from the date of the last departure from the endemic area (shortened from 12 months in 2020), provided they do not have symptoms of malaria [57]. The reduction to three months was based on a Centers for Disease Control and Prevention (CDC) analysis of surveillance reports of malaria cases imported to the United States.

This deferral applies even if travel was limited to travel through a malaria-endemic area en route to a malaria-free area, provided the time spent in the endemic area extended beyond 24 hours; common examples include passage through a malaria-endemic area to visit a tourist resort in a malaria-free area, passage through a malaria-endemic area to board a cruise ship, or on-shore excursions into a malaria-endemic area when traveling on a ship.

Risk-based deferral represents a compromise between prevention of transmission and acceptable levels of donor deferral. Chronic, asymptomatic Plasmodium infection is well described and can persist for months to even decades, conferring risk of TTM if those infected individuals proceed to donate. (See "Non-falciparum malaria: P. vivax, P. ovale, and P. malariae".)

Risk-based deferral has been effective in the United States where TTM is rare. Between 2000 and 2021, there were 13 reported cases of TTM in the United States for an estimated rate of <0.1 per million RBC units transfused [58,59].

Not all malaria-endemic areas pose equal risks. In one study, travel to Africa was estimated to present a risk for malaria infection >1000 times that of travel to endemic parts of Mexico [58]. Shortening the deferral period for visitors to Mexico from 12 to 3 months was estimated to increase the risk of collecting a unit with potential to transmit malaria by one unit every 57 years, at an annual gain of more than 56,000 donations. Given these data and the epidemiology of malaria in Mexico, donors are not required to be deferred after visiting specific areas of Mexico that have been determined to have no malarial transmission.

●Pathogen inactivation as a substitute for deferral in some cases – Use of a pathogen inactivation technology (available for platelets and plasma but not for whole blood or RBC units) is an alternative to donor deferral for travelers to a malaria-endemic area but not for individuals who have resided in a malaria-endemic country or who have had malaria. (See "Pathogen inactivation of blood products", section on 'Malaria and other parasites'.)

However, the major risk with Plasmodium is from RBCs and whole blood, as the parasite is primarily intra-erythrocytic. Pathogen inactivation technologies have not been approved for RBCs and whole blood in the United States but may be available in European countries. (See "Pathogen inactivation of blood products", section on 'RBCs and whole blood'.)

Babesiosis — Babesia is screened in the United States by selective laboratory testing in states with a higher prevalence of babesiosis. Donor history questions related to babesiosis are used in selected states. General questions about active infection may identify some infected individuals. (See "Blood donor screening: Laboratory testing", section on 'Babesia microti' and 'Symptoms of active infection' above.)

●Risk – Babesiosis is a tick-borne infection. Babesia is a parasite that infects RBCs, similar to malaria. There are over 100 species of Babesia, but only a few have been implicated in human infection; of which B. microti is overwhelmingly the most common. Babesia species are found in different geographic regions. B. microti is endemic in the Northeast and upper Midwest regions of the United States, as discussed separately. (See "Babesiosis: Microbiology, epidemiology, and pathogenesis" and "Babesiosis: Clinical manifestations and diagnosis".)

Transfusion-transmitted babesiosis (TTB) is mainly associated with RBC and whole blood units. It has not been associated with plasma. While rarely associated with whole blood derived platelets, most platelets in the United States are collected using apheresis technology for which the risk is low.

While most Babesia infections are often subclinical or characterized as a mild flu-like illness, some patients are at high risk of severe and even fatal infection, including those who are at extremes of age, immunocompromised, and/or asplenic.

Prior to adoption of regional testing for Babesia in the United States, TTB was considered a leading infectious risk to the United States blood supply [60]. (See "Blood donor screening: Laboratory testing", section on 'Babesia microti'.)

●Donor history questions in selected states – In states where Babesia blood donor laboratory testing is not done, donors are asked whether they had a positive laboratory test for babesiosis (either as part of a medical diagnosis or as part of blood donor screening) in the prior two years [61].

Questions about tick bite history are not asked as they are neither sensitive nor specific for babesiosis [62,63].

●Deferral criteria – Donors with a positive laboratory test result or diagnosis of babesiosis are deferred for two years after the positive test result, if the blood collection facility follows an approved laboratory testing protocol; alternatively, the donor may be deferred indefinitely (table 1).

●Pathogen inactivation as a substitute for deferral in some cases – Use of a pathogen inactivation technology (available for platelets and plasma but not for whole blood or RBC units) is an alternative to donor deferral for donors in states that perform laboratory testing for Babesia. (see "Pathogen inactivation of blood products", section on 'Malaria and other parasites')

However, the major risk with Babesia is from RBCs and whole blood, as the parasite is primarily intra-erythrocytic. Pathogen inactivation technologies have not been approved for RBCs and whole blood in the United States. (See "Pathogen inactivation of blood products", section on 'RBCs and whole blood'.)

Chagas disease — Chagas disease (American trypanosomiasis) is caused by infection with the protozoan parasite Trypanosoma cruzi. (See "Chagas disease: Epidemiology, screening, and prevention".)

●Risk – Chagas disease has rarely been reported to be transmitted by blood transfusion in the United States and Canada with fewer than 10 reported cases, almost exclusively due to platelet transfusions.

●Deferral criteria – Chagas disease is screened by laboratory testing of a donor's first donation. Medical history questions are not included in the donor history in the United States [64]. Donors with confirmed positive testing for T. cruzi are permanently deferred. (See "Blood donor screening: Laboratory testing", section on 'Chagas disease'.)

Prions (Creutzfeldt-Jakob disease, variant CJD) — Prion disorders such as Creutzfeldt-Jakob disease (CJD) are screened exclusively by the donor history; there is no laboratory testing of donors for these disorders.

●Risk – CJD is a rare, fatal, degenerative neurologic disorder caused by a prion. Prions are abnormal proteins that cause central nervous system neurodegenerative diseases known as transmissible spongiform encephalopathies (TSEs). CJD has a long asymptomatic latent period. Prions cannot be inactivated by conventional sterilization techniques or pathogen-reduction technologies. (See "Diseases of the central nervous system caused by prions", section on 'Pathogenesis of prion diseases'.)

Several forms of CJD are recognized. The hereditary forms due to germline genetic variants cannot be transmitted by transfusion; for the other forms, there is a theoretical risk. (See "Diseases of the central nervous system caused by prions".)

•vCJD – Variant Creutzfeldt-Jakob disease (vCJD) is the only form of prion disease that has been shown to be transfusion transmitted. This fatal degenerative neurologic disease was discovered in the United Kingdom in 1996 [65]. The prion that causes vCJD also causes bovine spongiform encephalopathy (BSE, also called "mad cow disease") [66].

Soon after the discovery of vCJD, four cases of probable transfusion transmission of the vCJD agent were reported in the United Kingdom. Three were associated with clinical disease, which developed from approximately 5 to 10 years after transfusion [67-72]. (See "Variant Creutzfeldt-Jakob disease".)

•iCJD – Iatrogenic CJD (iCJD) has occurred via human-to-human transmission with transplantation of dura mater, injection of pituitary-derived human growth hormone, corneal transplantation, and reuse of electroencephalography (EEG) electrodes, but not by blood transfusion. (See "Creutzfeldt-Jakob disease", section on 'Iatrogenic CJD'.)

Epidemiologic studies (including a review of mortality data in heavily transfused recipients, neuropathologic studies of deceased patients with hemophilia, and lookback studies assessing the health outcome of recipients who received blood components from donors who subsequently developed iCJD or other neurodegenerative disorders) have failed to establish a link between transfusion and transmission of types of CJD other than vCJD [73-76].

Despite a consensus that CJD is not transmitted by transfusion, it remains a theoretical risk due to its long incubation period [77,78].

●Deferral criteria – Updated donor deferral criteria for preventing possible transmission of CJD and vCJD by transfusion were published in a 2022 FDA guidance document [79].

Permanent/indefinite deferral applies to the following individuals (table 1):

•Ever diagnosed with CJD, vCJD, or other transmissible encephalopathy.

•Ever received a cadaveric dura mater transplant.

•Ever received bovine insulin or human growth hormone derived from cadaveric pituitary glands.

•Have any blood relative diagnosed with a heritable/genetic prion disease. (See "Diseases of the central nervous system caused by prions", section on 'Genetic CJD' and "Diseases of the central nervous system caused by prions", section on 'Gerstmann-Sträussler-Scheinker syndrome' and "Diseases of the central nervous system caused by prions", section on 'Fatal familial insomnia'.)

Previously, deferral criteria for possible vCJD exposure related to residence in or travel to Europe (or specific European countries) or other potential exposures were in place, but these deferral criteria were discontinued based on decreased prevalence in the general population.

Specifically, individuals who spent time in the United Kingdom, France, Ireland, and other countries in Europe during time intervals that previously were of concern, who have received blood transfusions in the three specified countries, or who injected bovine insulin from the United Kingdom or other countries with BSE, are no longer deferred [79].

PAST RESPONSES TO EMERGING INFECTIOUS DISEASES AND THEIR IMPACT ON DONOR SCREENING — 

During emerging infectious disease outbreaks, regulatory agencies and transfusion medicine services may institute donor history questions and/or laboratory testing to identify donors at increased risk of transmitting certain infectious pathogens.

Questions may be removed or modified for various reasons:

●The outbreak subsides.

●Evidence accumulates for lack of transfusion transmission.

●Questions are demonstrated not to provide additional risk reduction beyond other donor history questions or laboratory testing.

In some cases, more than one reason for removal may apply, such as for Zika virus. For many organisms, general donor history questions about fever or feeling unwell (table 2) will exclude actively infected donors. (See 'Symptoms of active infection' above.)

Selected examples include the following:

Outbreaks that have subsided

●Zika virus — Zika virus is a mosquito-borne flavivirus (the same virus family that includes West Nile and dengue viruses). Infected persons are usually asymptomatic; they may have a mild febrile illness or more serious outcomes, especially during pregnancy. (See "Zika virus infection: An overview".)

Four transfusion recipients were reported during the 2015 to 2016 outbreak in the Americas to test positive for Zika virus RNA without clinical symptoms [80,81]. Testing had been performed after a donor reported post-donation symptoms compatible with an arboviral illness that was subsequently diagnosed as Zika virus infection.

At that time, several United States and international agencies issued guidance to reduce the risk of transmission based on symptoms, travel history, or sexual activity [82]. Donor history questions and deferral guidance were eliminated after laboratory testing was instituted. Testing was discontinued in 2021 after the outbreak waned; there were no further active infections in the United States, and it was determined that evidence of clinical risk from transfusion-transmitted infection was very low [83,84]. (See "Blood donor screening: Laboratory testing", section on 'Zika virus'.)

Infections that are not transfusion transmitted

●COVID-19 – There have been no reported cases of transfusion-transmitted infection from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease 2019 (COVID-19). General donor history questions about active infection may exclude acutely ill individuals. (See 'Symptoms of active infection' above.)

The US Food and Drug Administration (FDA) does not recommend testing donated blood for the virus, as respiratory viruses are not known to be transmitted by transfusion [85]. (See "COVID-19: Epidemiology, virology, and prevention", section on 'Transmission'.)

There are no specific questions about COVID-19. If a donor volunteers that they have a history of COVID-19 or a positive test for SARS-CoV-2 (antibody, antigen, or nucleic acid), these are not considered exclusions to donation as long as one of the following criteria is met [85]:

•If symptomatic, the illness resolved >10 days prior to donation (reduced from 14 days in earlier guidance).

•If asymptomatic with a positive test, the last positive test was >10 days prior (reduced from 14 days in earlier guidance).

For individuals with possible COVID-19 without confirmatory testing, the FDA suggests that individuals refrain from donating blood for 10 days after either of the following:

•Symptoms have resolved.

•The last possible close contact with an infected individual has occurred.

Donors are encouraged to contact the blood center if they develop symptoms compatible with COVID-19 or are diagnosed with COVID-19 in a defined period after donation (ranging from 48 hours to 14 days depending on the blood center). Units from these individuals are discarded.

●Mpox – Despite some focal outbreaks of mpox (previously monkeypox) infection, there have been no reports of mpox transmission from blood transfusion, and the US Food and Drug Administration (FDA) has not recommended that blood donors be asked specific questions about exposure to monkeypox virus [86].

●Oropouche virus (OROV) – In the summer of 2024, The US Centers for Disease Control and Prevention (CDC) noted an increase in Oropouche virus (OROV) in the Americas region; this is an infection spread by the bite of an insect vector (biting midge, also called "no-see-um"). (See "Oropouche virus infection", section on 'Transmission'.)

There have been no reports of transfusion transmission of OROV, and the FDA has not recommended that blood donors be asked specific questions about exposure to OROV [87].

●Ebola virus – Ebola virus causes hemorrhagic fever with a high mortality rate. Outbreaks of Ebola occur periodically in several parts of Africa. According to the FDA, donor questioning about travel history, residence, or symptoms would be triggered if a specific country in Africa is classified as having "widespread transmission of Ebola." (See "Epidemiology and pathogenesis of Ebola disease".)

Other examples of agents that gave rise to questions that have since been rescinded include leishmaniasis (no evidence for transfusion transmission in the United States) and xenotropic murine leukemia virus-related virus (XMRV), which was determined not to cause human infection [88].

SCREENING FOR NON-INFECTIOUS RISKS

History of cancer — Transmission of cancer from a donor to a recipient has not been reported.

The US Food and Drug Administration (FDA) makes no recommendations about prospective donors with cancer and does not require that blood centers ask questions concerning a history of cancer. Standards from the Association for the Advancement of Blood & Biotherapies (AABB) state that the prospective donor must be in good health and free of major organ diseases such as cancer; furthermore, a question regarding a history of cancer is included on the Uniform Donor History Questionnaire (UDHQ).

However, donors are questioned about active cancer, since many transfusion recipients are immunosuppressed and there is a theoretical risk that malignant cells could engraft in the recipient.

●Deferral criteria – The blood center's medical director determines the center's deferral policy (table 1). Most blood centers use the following criteria based on the type of malignancy [89]:

•Solid organ cancer – Deferral until the donor has been symptom free and considered to be clinically cured for a defined time period (typically one to five years, depending on the blood center).

•Hematologic cancer – Permanent deferral.

•Localized cancer that cannot spread hematogenously – No deferral once the cancer has been excised. Examples include basal cell cancer of skin and cervical carcinoma in situ.

●Supporting evidence – Available data regarding transfusion of components from donors subsequently diagnosed with malignancy include:

•A retrospective series of over 350,000 transfusion recipients in Denmark and Sweden from the ScanDat database identified 12,012 transfusion recipients (3 percent) who were exposed to blood products from donors who subsequently developed cancer and were considered to have subclinical cancer at the time of the donation [90]. The adjusted risk of cancer in the recipients from these donors was not increased (adjusted relative risk [RR] 1.00, 95% CI 0.94-1.07). A second study using the ScanDat database showed no transmission of chronic lymphocytic leukemia (CLL) to recipients of blood from donors who later developed CLL [91].

•A series of 105 individuals who were exposed to blood products from donors with hematologic malignancies (leukemia or lymphoma) were followed for >7 years, and none developed a hematologic malignancy [92].

•A case report described transfusion from a donor who was subsequently diagnosed with chronic myeloid leukemia (CML) [93]. The DNA sequence from the CML clone was detectable in the recipient's blood for 75 days. The recipient died eight months after the transfusion from an unrelated cause, so the significance of this finding remains unknown.

Neurodegenerative and other neurologic disorders — The medical history questionnaire does not include specific questions about neurodegenerative or neurologic conditions, with the exception of prion disorders. (See 'Prions (Creutzfeldt-Jakob disease, variant CJD)' above.)

If the donor volunteers during the screening process that they have been diagnosed with Alzheimer disease or Parkinson disease, their eligibility for donation is based on an assessment by the blood donation facility staff of whether the donor has the cognitive ability to provide reliable answers to the screening questions and whether the donor is physically able to tolerate the donation procedure. (See "Blood donor screening: Overview of recipient and donor protections", section on 'Protection of the donor'.)

Supporting evidence includes:

●Neurodegenerative disorders – The risk of transfer of a neurodegenerative disorder (Alzheimer disease, Parkinson disease) from blood products does not appear to be increased.

In a retrospective study involving over 1.4 million transfusion recipients, 2.9 percent received a transfusion from a donor who was diagnosed with dementia of any kind, Alzheimer disease, or Parkinson disease [76]. There was no increased risk of recipients developing dementia (hazard ratio [HR] 1.04, 95% CI 0.99-1.09), Alzheimer disease (HR 0.99, 95% CI 0.85-1.15), or Parkinson disease (HR 0.94, 95% CI 0.78-1.14).

●Amyloid-associated intracerebral hemorrhage (ICH) – Spontaneous ICH may be a surrogate cerebral amyloid angiopathy (CAA), which can occur in persons with Alzheimer disease. (See "Cerebral amyloid angiopathy", section on 'Acute intracerebral hemorrhage' and "Epidemiology, pathology, and pathogenesis of Alzheimer disease", section on 'Pathology'.)

A large retrospective exploratory study from 2023 was published by the same group that published the above study, using their updated donor/recipient database to evaluate risk of ICH in transfusion recipients from RBC donors with ≥2 episodes of spontaneous ICH [94]. Among >100,000 transfusion recipients, the adjusted hazard ratio (HR) for ICH in transfusion recipients whose blood donors had ≥2 episodes of ICH was 2.3 to 2.7, compared with recipients whose donors had a single ICH or no ICH. Although these results support the theoretical possibility of a transmissible factor for CAA, the number of such possible transmissions was low, and the study did not provide definitive proof of such transmission, especially since investigators were unable to identify a plausible mechanism [95].

Other medical conditions — Other medical conditions that could result in risks to the donor and donor protections are discussed separately. An international survey demonstrated substantial variation among blood centers in deferral policies for a number of donor medical conditions [96]. (See "Blood donor screening: Overview of recipient and donor protections", section on 'Protection of the donor'.)

Medications taken by the donor — Most medications taken by donors pose no known risks to recipients. In most cases, only small quantities of drugs are present in a unit of blood, and the drugs will undergo significant dilution in the recipient's plasma volume.

However, donors taking certain medications are deferred, either for a defined period of time after stopping the medication or indefinitely.

●Medications that indicate possible infectious risk are discussed above. (See 'Recent incarceration, vaccination, antibiotics, or antiviral medications' above.)

●The possibility of allergic reactions in a recipient related to substances ingested by the donor is discussed separately. (See "Immunologic transfusion reactions", section on 'Allergic reactions'.)

Potential teratogens — Some drugs may pose a risk to transfusion recipients who may become pregnant, due to their demonstrated teratogenic potential at low concentrations. Information from the AABB specifies the following deferral intervals following discontinuation of the medication [22]:

●Acitretin (Soriatane), used for psoriasis – 36 months

●Dutasteride (Avodart, Jalyn), used for benign prostatic hypertrophy – 6 months

●Etretinate (Tegison), used for psoriasis – indefinite

●Finasteride (Propecia, Proscar), used for benign prostatic hypertrophy and hair regeneration – 1 month

●Isotretinoin (Accutane, Amnesteem, Absorica, Claravis, Myorisan, Sotret, Zenatane), used for acne – 1 month

●Leflunomide (Arava), used for rheumatoid arthritis – 24 months

●Mycophenolate mofetil (CellCept), used for immunosuppression – 6 weeks

●Sonidegib (Odomzo), used for basal cell carcinoma – 24 months

●Teriflunomide (Aubagio), used for multiple sclerosis – 24 months

●Thalidomide (Thalomid), used for multiple myeloma – 1 month

●Upadacitinib (Rinvoq), used for rheumatoid arthritis – 1 month

●Vismodegib (Erivedge), used for basal cell carcinoma – 24 months

The donor history is the only means of identifying these exposures; there is no routine testing for these medications.

Antiplatelet drugs and anticoagulants — Information from the AABB specifies deferring donors for platelet apheresis donation if any of the following antiplatelet medications were taken within the following timeframes [22]:

●Aspirin, aspirin-containing drugs, or piroxicam – Previous 2 days

●Prasugrel – Previous 3 days

●Ticagrelor – Previous 7 days

●Clopidogrel or ticlopidine (not available in the United States) – Previous 14 days

●Vorapaxar – Previous 1 month

This donation restriction is specific to platelet apheresis donors and does not apply to whole blood donors, unless platelets made from that unit of whole blood will be the sole source of platelets for a given patient. This would apply only to whole blood derived platelet transfusions designated for neonatal and young pediatric recipients.

The donor history is the only means of identifying these exposures; there is no routine quality control testing of platelet function or clotting tests for platelet apheresis products. This is due in part to the inability of in vitro platelet function testing to accurately predict in vivo platelet function.

The deferral period for individuals taking an anticoagulant is based on two factors: the concern that the donor may have excessive bleeding at the venipuncture site and the potential effect of the anticoagulant on the clotting properties of the donated plasma. Donors taking anticoagulants are uniformly deferred from platelet apheresis donation. However, some blood centers may elect to collect whole blood from such donors if they judge the bleeding risk at the phlebotomy site to be minimal and if they have a method to be sure that the plasma derived from such collections (which would have impaired coagulation properties) is not used for transfusion.

Timeframes are as follows for anticoagulants [22]:

●Direct oral anticoagulants (DOACs; apixaban, dabigatran, edoxaban, rivaroxaban), fondaparinux, and the low molecular weight (LMW) heparins dalteparin and enoxaparin – Previous two days.

●Warfarin and LMW heparins other than dalteparin and enoxaparin – Previous seven days.

SOCIETY GUIDELINE LINKS — 

Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Transfusion and patient blood management".)

INFORMATION FOR PATIENTS — 

UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topic (see "Patient education: Blood donation (giving blood) (The Basics)")

●Beyond the Basics topic (see "Patient education: Blood donation (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

●Importance of the history – The donor history is critical to safety of the blood supply. Individuals >16 to 17 years (depending on the state) are able to donate blood provided they complete a donor history questionnaire and do not meet criteria for deferral (table 2). The questionnaire is typically done verbally at the donation center, but some centers use computer-assisted methods and/or allow use of an online portal on the day of donation. (See 'Introduction' above and 'Overview' above.)

●General questions related to infectious risk – Donors are asked about symptoms of active infection; recent vaccinations, antibiotics, certain antiviral medications; and recent piercings, tattoos, and transfusions. Positive answers usually result in temporary deferral; piercings and tattoos done in certain types of facilities do not require deferral. (See 'General infectious disease screening questions' above.)

●Questions and deferrals for specific pathogens – Questions are used to identify donors at increased risk of transmitting certain infections, with specific deferral periods summarized in the table (table 1).

•Viruses – Questions relate to HIV (gender-neutral individualized risk assessment based on sexual history and other bloodborne exposures) and hepatitis B and C. A question about West Nile virus was previously included and later removed. The table summarizes risks of transfusion-transmitted viral infections (table 3). (See 'Viruses' above.)

•Bacteria – A positive response to a question about syphilis or gonorrhea diagnosis and treatment will lead to a temporary deferral. (See 'Bacteria' above.)

•Parasites – Malaria risk reduction differs between endemic and non-endemic countries. In non-endemic countries, questions include malaria history, previous residence in a malaria-endemic country, and travel. For babesiosis, blood collection agencies in states that do not perform Babesia laboratory testing ask donors about positive laboratory testing for babesiosis in the prior two years. Deferral periods for malaria and babesiosis depend on specific answers. Chagas disease is evaluated solely by laboratory testing. (See 'Parasites' above.)

Pathogen inactivation technologies are an alternative to donor deferral for travelers to malaria endemic countries, but this technology only applies to plasma and platelets, whereas RBCs and whole blood carry the greatest risk of transmission. (See "Pathogen inactivation of blood products".)

•Prions – Variant Creutzfeldt-Jakob disease (vCJD) is the only prion disease shown to be transfusion transmitted, but theoretical risks exist for other prion diseases. Donors are asked about previous diagnoses, cadaveric transplants, and other risks and are permanently deferred if any risk factor is present. (See 'Prions (Creutzfeldt-Jakob disease, variant CJD)' above.)

●Pathogens that are not queried – Some infections are not specifically queried, either because an outbreak has subsided (Zika virus, Ebola virus) and/or there is no evidence of transfusion transmission (COVID-19, mpox, Oropouche virus). (See 'Past responses to emerging infectious diseases and their impact on donor screening' above.)

●Non-infectious risks – These include history of cancer, neurodegenerative diseases, and medications listed above that are potentially teratogenic, could cause bleeding, or suggest a possible increased noninfectious risk. (See 'History of cancer' above and 'Neurodegenerative and other neurologic disorders' above and 'Other medical conditions' above and 'Medications taken by the donor' above.)

●Other aspects of donor screening – The history is complemented by a limited physical examination (vital signs, skin check), laboratory screening for selected pathogens, and other evaluations, as discussed separately. (See 'Overview' above and "Blood donor screening: Laboratory testing" and "Blood donor screening: Overview of recipient and donor protections".)

ACKNOWLEDGMENT — 

We are saddened by the death of Arthur J Silvergleid, MD, who passed away in April 2024. The UpToDate editorial staff gratefully acknowledges the extensive contributions of Dr. Silvergleid to earlier versions of this and many other topic reviews.

Dr. Bloch is a member of the US Food and Drug Administration (FDA) Blood Products Advisory Committee. The views expressed in this topic are those of the author(s) and do not reflect the official views of the Blood Products Advisory Committee or the formal position of the FDA and also do not bind or otherwise obligate or commit either the Advisory Committee or the FDA to the views expressed.