Version July 2025
INTRODUCTION —
Accurate measurement and interpretation of blood pressure is essential in the diagnosis and management of hypertension.
Blood pressure measurement methods include office-based blood pressure measurement, self-measured blood pressure (SMBP), and ambulatory blood pressure monitoring (ABPM). While office-based blood pressure measurement is the most frequently used method for the diagnosis and management of hypertension, ABPM and SMBP most accurately reflect daily blood pressure throughout the day. ABPM and SMBP are also necessary to evaluate for white coat and masked hypertension. In addition, ABPM is a better estimate of cardiovascular risk when compared with the other methods due to its ability to capture nighttime blood pressures [1-3]. It is therefore an important tool for diagnosing hypertension and monitoring selected patients on therapy.
This topic presents the indications, procedure, and interpretation of ABPM. The appropriate technique for office-based blood pressure and SMBP is discussed separately. (See "Hypertension in adults: Blood pressure measurement and diagnosis", section on 'Methods for measuring blood pressure'.)
The diagnosis of hypertension, including the role of ABPM in establishing the diagnosis, is reviewed in further detail separately. (See "Overview of hypertension in adults" and "Hypertension in adults: Blood pressure measurement and diagnosis", section on 'Diagnosis of hypertension'.)
ABPM AND BLOOD PRESSURE MANAGEMENT —
ABPM is performed using a wearable device prescribed by the clinician. The device takes blood pressure measurements over a 24- to 48-hour period, usually every 15 to 30 minutes during the daytime and every 30 to 60 minutes during the night [4]. Blood pressure measurements are recorded on the device, and the average day (diurnal) or night (nocturnal) pressures are calculated by a computer. The percentage of blood pressure readings exceeding the upper limit of normal can also be determined.
ABPM captures the effects of normal daily activities on blood pressure, provides information on the behavior of blood pressure during sleep, and provides a greater number of readings than can be obtained during a typical office encounter.
Indications — Usually, ABPM is performed to determine whether office-based blood pressure and out-of-office blood pressure measurements are discordant. Additional indications include the following:
●Diagnosis of hypertension in patients with elevated office-based blood pressure. (See "Hypertension in adults: Blood pressure measurement and diagnosis".)
●Diagnosis of white coat hypertension or masked hypertension (table 1) in patients with discordant office-based and self-measured blood pressure readings. (See "Hypertension in adults: Blood pressure measurement and diagnosis", section on 'White coat hypertension' and "Hypertension in adults: Blood pressure measurement and diagnosis", section on 'Masked hypertension'.)
●Detection of nocturnal hypertension.
●Detection of episodic hypertension or hypotension.
●Surveillance and monitoring for patients with confirmed white coat hypertension, white coat effect, masked hypertension, and masked uncontrolled hypertension (table 2). As an example, given the high likelihood of sustained hypertension developing in patients with white coat hypertension, ABPM is repeated annually (or every two years for younger patients). (See "Hypertension in adults: Blood pressure measurement and diagnosis", section on 'White coat hypertension' and "Hypertension in adults: Blood pressure measurement and diagnosis", section on 'Masked hypertension'.)
Limitations — Accessibility to ABPM remains limited due to several factors, including lack of awareness, practice start-up expenses, and lack of insurance coverage in many settings. As eligibility criteria and cost evolve and more primary care practices prioritize investment in ABPM, access to ABPM may become more widespread [5,6].
Contraindications — ABPM is contraindicated in patients with atrial fibrillation or other irregular arrhythmia, severe clotting disorders, or latex allergy. ABPM is also contraindicated in patients who cannot have blood pressure measured in either arm (eg, missing limbs or bilateral lymphedema).
ABPM PROCEDURE
Availability — Specialty hypertension clinics and a growing number of primary care offices have ABPM programs in place. Guidance for implementing office-based ABPM programs and the selection of ABPM devices have been summarized in the literature [7,8]. Validated device listings are also available online through Validated Device Listing, Hypertension Canada, and STRIDE BP.
If a local office-based ABPM program is not available, ABPM may also be arranged by mail through a third-party service.
Configuring the monitor before use — Clinical staff must manually enter the desired measurement settings for each patient. This is typically done during the day-1 visit (when the patient arrives to receive the monitor).
Most clinical centers set the monitor to measure blood pressure every 15 to 30 minutes during the day and every 60 minutes during the night. The default setting for nighttime hours is usually from 10 PM to 6 AM; however, these can be reconfigured with the patient's usual bedtime and wake time. Some monitors allow the patient to manually enter nighttime hours.
There is also an option to set an alert sound issued by the monitor approximately five seconds prior to inflation. This sound prompts the patient to relax their arm by their side to facilitate accurate readings. The warning sound can be disabled at night to minimize sleep disruption.
The screen may be programmed to display or conceal the blood pressure readings. There is no consensus on this configuration option. Some experts suggest that blinding the patient to blood pressure measurements may help mitigate any anxiety that may occur as a result of high readings.
Monitor application and operation — Patients should arrive ready to have the monitor applied, wearing a short-sleeved shirt to facilitate cuff application to a bare arm.
In most patients, the cuff is applied to the nondominant arm by the clinician or trained staff, with the attached inflation/recording unit worn on the opposite hip using either a belt or an over-the-shoulder strap. The cuff is applied to the contralateral (dominant) arm if any of the following are present in the nondominant arm:
●Lymphedema or prior axillary node dissection. (See "Screening for and prevention of breast cancer-related lymphedema", section on 'Approach to venipuncture and blood pressure monitoring'.)
●Arteriovenous fistula.
●Systolic or diastolic blood pressure is consistently 10 mmHg lower in the nondominant arm versus the dominant arm when measured using standardized office-based measurement or self-measured blood pressure.
At least two inflations of the ABPM unit should be obtained in the office to familiarize the patient with how the device works and feels. ABPM readings can be triggered manually (in addition to the preprogrammed timed readings) by pressing the unit's "manual blood pressure" button. Readings should be verified against a same-day standardized office-based reading to confirm accuracy. (See "Hypertension in adults: Blood pressure measurement and diagnosis", section on 'Methods for measuring blood pressure'.)
The monitor measures blood pressure according to the programmed schedule (eg, every 30 minutes during the day and every 60 minutes at night). On most monitors, an individual measurement may be stopped if it commences at an inconvenient time. If a reading is skipped, the internal timer will reset the device to take the next blood pressure reading as scheduled.
If the device is unable to assess the blood pressure accurately, it will try to measure it a second time. If the second attempt is unsuccessful, the monitor will not attempt a third cuff inflation but will instead try again after the preset time interval.
The device must be returned for the report to be generated. Some devices are returned to the clinic, whereas others are mailed. If the patient is expected to remove the device on their own, they should be instructed on when it is appropriate to do so.
Patient instructions
●The monitor session is for 24 hours, and it is preferable not to remove it during this time.
●Avoid bathing or showering while wearing the monitor. The monitors are not waterproof.
●Cuff inflation may cause some discomfort, even with the use of an appropriately sized cuff.
●When a measurement commences, keep the arm relaxed, still, and at the side. Individual measurements may be skipped if they occur at an inconvenient time; however, it is best to skip measurements as infrequently as possible.
●While wearing the monitor, patients should record their bedtime, their wake time, the timing of naps, and the times that antihypertensive medications are taken. They should also record the timing of exercise, stressful situations (eg, work presentations), or any symptoms potentially attributable to their blood pressure, like headaches or lightheadedness.
●When the 24-hour session is complete, the monitor should be removed and returned as instructed by the clinical staff.
INTERPRETATION OF THE ABPM REPORT
The ABPM report — ABPM reports include the number of daytime, nighttime, and total readings obtained; averages of daytime, nighttime, and 24-hour blood pressures; and heart rates. The percentage of blood pressure readings exceeding the upper limit of normal can also be determined. The ABPM study results are summarized in a report (figure 1) mapping systolic and diastolic blood pressures over the 24-hour session. ABPM software usually allows the addition of patient diary notes, including the timing of antihypertensive medications, exercise, stressful situations, and symptoms (eg, headaches, lightheadedness).
Failed measurements and outlier readings (due to artifacts or grossly erroneous readings) are generally excluded. While there is no consensus regarding the minimal number of readings required for a valid 24-hour ABPM assessment, several guidelines suggest a minimum of 70 percent of successful programmed measurements, often corresponding to a minimum of 20 daytime readings and 7 nighttime readings [9,10]. If the number of measurements obtained is only slightly less than this, it may still be reasonable to accept the ABPM study as valid, although not optimal. If the number of measurements obtained is substantially less than this, we would repeat the ABPM study.
Comparing ABPM with office-based readings — The ABPM report is compared with standardized office-based blood pressure measurements to determine whether they are consistent or discordant. If there is discordance, the patient should be evaluated for masked or white coat hypertension (table 2), depending upon whether the ABPM measurements are above or below the threshold for hypertension. White coat and masked hypertension are discussed in further detail separately. (See "Hypertension in adults: Blood pressure measurement and diagnosis", section on 'White coat hypertension' and "Hypertension in adults: Blood pressure measurement and diagnosis", section on 'Masked hypertension'.)
Diagnosing hypertension — Hypertension is diagnosed with ABPM when the 24-hour average blood pressure is ≥125/75 mmHg or the average daytime blood pressure is ≥130/80 mmHg. Nocturnal hypertension is present when the average nighttime blood pressure is ≥110/65 mmHg (table 3). These definitions are consistent with those from the American College of Cardiology/American Heart Association [11].
Blood pressure measurement and the diagnosis of hypertension using ABPM are discussed in further detail separately. (See "Hypertension in adults: Blood pressure measurement and diagnosis", section on 'Options for establishing the diagnosis'.)
Nocturnal dipping and other data — The ABPM report also provides data regarding the proportional decrease in nighttime compared with daytime blood pressure (ie, nocturnal "dipping"), overall blood pressure variability throughout the day, blood pressure in the transition from nighttime to morning blood pressure (ie, blood pressure "surge"), and the proportion of time during the day when systolic and/or diastolic blood pressures are elevated (termed systolic and diastolic "blood pressure load").
Of these measurements, nocturnal dipping is noteworthy because the absence of dipping is an independent risk factor for heart failure and other cardiovascular complications [12-17]. In both normotensive and hypertensive patients, the average nighttime systolic and diastolic blood pressure is approximately 15 percent lower than the daytime value (figure 1) [18]. Failure of the blood pressure to fall by at least 10 percent during sleep is called "nondipping" (figure 2).
In one large cohort study, the risk of heart failure among nondippers was more than twice that of dippers (hazard ratio 2.21, 95% CI 1.12-4.36), even after controlling for office-based blood pressure and other factors [17]. In addition, in patients with diabetes, nondipping is associated with the progression of nephropathy; nondipping is also associated with a more rapid decline in kidney function and risk for end-stage kidney disease among patients with chronic kidney disease [2,19-21].
The underlying mechanisms of nondipping are unknown, but intrinsic kidney defects may contribute [22-24]. Melatonin deficiency and sleep apnea may also have a role.
SUMMARY AND RECOMMENDATIONS
●Description and indications – Ambulatory blood pressure monitoring (ABPM) is the blood pressure measurement method that most accurately reflects daily blood pressure and associated cardiovascular risk. ABPM is an important tool for diagnosing hypertension, white coat hypertension, and masked hypertension and for monitoring selected patients on therapy.
ABPM is performed using a wearable device. The device takes blood pressure measurements over a 24- to 48-hour period, usually every 15 to 30 minutes during the daytime and every 30 to 60 minutes during sleep. (See 'ABPM and blood pressure management' above.)
●Procedure
•Availability – ABPM can be arranged in the clinician's office or by mail (through a third party). (See 'Availability' above.)
•Configuring the monitor before use – Measurement settings must be manually entered. Most clinical centers set the monitor to measure blood pressure every 15 to 30 minutes during the day and every 30 to 60 minutes during the night, although these can be reconfigured with the patient's usual bedtime and wake time. (See 'Configuring the monitor before use' above.)
•Monitor application and operation – The cuff should be applied to the nondominant arm when possible. For patients who have a reason to avoid blood pressure measurements on their nondominant arm (eg, lymphedema, prior axillary lymph node dissection, arteriovenous fistula), the contralateral arm should be used. At least two inflations of the ABPM unit should be obtained in the office so that the patient becomes comfortable with how the device works. (See 'Monitor application and operation' above.)
•Patient instructions – Patients should be provided with instructions for the ABPM session, including removal instructions when the session is complete. They should avoid bathing, showering, or getting the monitor wet. Patients should also record the timing of sleep, waking up, activities, timing of antihypertensive medications, and symptoms. (See 'Patient instructions' above.)
●Interpretation – A valid study typically requires a minimum of approximately 20 daytime readings and 7 nighttime readings. (See 'Interpretation of the ABPM report' above.)
•Diagnosing hypertension – Hypertension is diagnosed or excluded using the average 24-hour blood pressure, average daytime (awake) blood pressure, and average nighttime (asleep) blood pressure (figure 1). The definition of hypertension based on blood pressure measurement strategy is reviewed in the table (table 3) and discussed in further detail separately. (See 'Diagnosing hypertension' above and "Hypertension in adults: Blood pressure measurement and diagnosis", section on 'Diagnosis of hypertension'.)
•Nocturnal dipping – The ABPM report also provides additional blood pressure data throughout the day, including the presence of nocturnal dipping. Dipping is the proportional decrease in nighttime compared with daytime blood pressure (reported as the percentage decline); in most patients, the average nighttime systolic and diastolic blood pressure is approximately 15 percent lower than the daytime value. Failure of the blood pressure to fall by at least 10 percent during sleep is called "nondipping." Nondipping is an independent risk factor for heart failure and other cardiovascular complications. (See 'Nocturnal dipping and other data' above.)
ACKNOWLEDGMENTS
The UpToDate editorial staff acknowledges Norman M Kaplan, MD, who contributed to earlier versions of this topic review.
We are saddened by the death of George Bakris, MD, who passed away in June 2024. UpToDate acknowledges Dr. Bakris's past work as a section editor for this topic.
