TB Skin Test Interpretation in HIV/AIDS and Immunocompromised Patients

Introduction to TB Skin Test Interpretation

The American Thoracic Society recommends that a tuberculin skin test (TST) induration of ≥5 mm is considered positive and indicates M. tuberculosis infection requiring evaluation for active TB and treatment for latent TB infection if active disease is excluded in HIV-infected and other immunocompromised patients 1, 2, 3, 4

The Centers for Disease Control and Prevention (CDC) states that HIV-infected persons require a ≥5 mm induration cutoff regardless of CD4 count 1, 2, 3, 4
The CDC also recommends that recent close contacts of persons with active pulmonary or laryngeal TB should be considered high-risk patients 1, 2, 4
Organ transplant recipients and other immunosuppressed patients receiving the equivalent of >15 mg/day of prednisone for ≥1 month should also be considered high-risk patients 1
Persons with fibrotic changes on chest radiograph consistent with prior TB should be considered high-risk patients 4

The CDC recommends that anergy testing is not recommended for routine use in HIV-infected or other immunocompromised persons due to lack of standardization, poor reproducibility, and no documented benefit in screening programs for M. tuberculosis infection 1, 5, 6
The TST has a reported 25% false-negative rate during initial evaluation of active TB 4

The American Thoracic Society recommends that TSTs should be read between 48-72 hours after injection when induration reaches maximum size 1, 2, 3, 4
The CDC states that tests read after 72 hours underestimate true induration size 4
The CDC also recommends that only induration (hardened area), NOT erythema (redness), should be measured 1, 3, 4

The American Thoracic Society recommends that for any positive TST (≥5 mm in HIV/immunocompromised), a chest radiograph should be obtained to exclude active pulmonary TB 1, 2, 3
The CDC states that clinical evaluation for TB symptoms (cough, fever, night sweats, weight loss) should be performed 1, 2
The CDC also recommends that sputum samples should be obtained if symptoms are present or radiograph is abnormal 1, 2

The CDC recommends that positive TST in BCG-vaccinated patients should not be dismissed—tuberculin skin testing is not contraindicated in BCG recipients, and positive reactions should be interpreted as M. tuberculosis infection when the person is at increased risk 1, 4
The CDC states that anergy testing should not be relied on to guide treatment decisions in HIV/immunocompromised patients 1, 5, 6
The CDC also recommends that only induration, not erythema, should be measured and recorded 3, 4
The CDC states that patient self-reading of results is unacceptable 3, 4
The CDC recommends that reading should not be delayed beyond 72 hours, as this reduces accuracy 3, 4