Version July 2025
| Tuberculin skin test reaction size (mm) | Situation in which reaction is considered positive* |
| <5 | HIV infection plus close contact of active contagious case¶ |
| ≥5 | HIV infection |
| Close contact of active contagious case | |
| Abnormal chest radiograph with fibrotic changes consistent with old TB | |
| Immunosuppressed patients: TNF-alpha inhibitors, chemotherapy, organ transplantation, glucocorticoid treatment (equivalent of ≥15 mg/day prednisone for ≥1 month) | |
| ≥10 | Persons with clinical conditions that increase the risk of reactivation, including silicosisΔ, chronic renal failure requiring dialysisΔ, diabetes mellitus, some malignancies (leukemias, lymphomas, carcinoma of the head, neck, or lung), underweight (by ≥10% ideal body weight), jejunoileal bypass, injection drug users |
| Children age <4 years◊ | |
| Foreign-born from countries with incidence >25/100,000§ | |
| Residents and employees in high-risk settings, such as prisons, jails, health care facilities, mycobacteriology labs, and homeless shelters | |
| ≥15 | Healthy individuals age ≥4 years with low likelihood of true TB infection¥ |
TB: tuberculosis; TNF: tumor necrosis factor; TST: tuberculin skin test.
* The goal of testing for TB infection is to identify individuals who are at increased risk for the development of TB disease and therefore would benefit from treatment of TB infection. Only those who would benefit from treatment should be tested, so a decision to test presupposes a decision to treat if the test is positive. Refer to the UpToDate topic on diagnosis of TB infection for discussion of issues related to interpretation of repeat TST.
¶ The risk of active TB is high among human immunodeficiency virus (HIV)-positive patients who are close contacts of active contagious cases and are anergic.
Δ The United States Centers for Disease Control and Prevention (CDC) recommends a 10 mm induration definition for patients with silicosis or chronic renal failure. However, population-based studies demonstrate that the relative risk for development of tuberculosis disease in this category is high (≥10× that of healthy individuals). For this reason, many favor a lower threshold for a positive test (≥5 mm).
◊ The American Academy of Pediatrics (AAP) favors a threshold of 10 mm for otherwise healthy children <4 years of age with no risk factors (and a threshold of ≥15 mm for healthy children ≥4 years of age)[1]. This threshold differs from the CDC which favors a threshold of 10 mm for otherwise healthy children <5 years of age (and a threshold of ≥15 mm for healthy children ≥5 years of age)[2].
§ The United States Preventive Services Task Force recommends screening of adults at risk for TB infection (implying all foreign-born adults from countries with high TB incidence), regardless of time since immigration[3]; this approach is based on a 2023 systematic review[4]. Previously, the CDC favored testing only for foreign-born individuals (regardless of age) who immigrated within the past five years, given the higher risk of disease within the first five years after immigration.
¥ Individuals with a low likelihood of true TB infection should not be tested routinely unless they are entering a high-risk setting such as starting employment at a healthcare facility. A threshold of 15 mm is used in the United States and is appropriate for healthy individuals with low likelihood of true TB infection and high likelihood of exposure to nontuberculous mycobacteria (eg, southern United States). However, Canadian guidelines use a threshold of 10 mm for healthy individuals given the lower likelihood of exposure to nontuberculous mycobacteria. (Refer to the UpToDate topic on epidemiology of nontuberculous mycobacterial infections.)