Timing of Tuberculin Skin Testing

Post-Exposure Testing

The American Thoracic Society recommends administering a second tuberculin skin test 8-12 weeks after the last exposure to an infectious TB patient for contacts with an initially negative test result 1
The initial test may be negative even if the person is infected because the immune response has not yet developed, and tuberculin sensitivity may take 8-10 weeks to appear after M. tuberculosis infection 1
High-risk contacts, such as children younger than 5 years and HIV-infected or immunocompromised individuals, should receive preventive treatment while awaiting the second test 1
If the second test remains negative (≥5 mm) and the contact is immunocompetent with no ongoing exposure, preventive treatment may be discontinued 1
If the second test is negative but the contact is immunocompromised, complete the full course of preventive therapy 1

The Centers for Disease Control and Prevention recommends two-step testing for newly employed healthcare workers with an initial negative PPD and no documented negative test within the preceding 12 months 2
Two-step testing is also recommended for individuals in settings with periodic TB screening, such as healthcare facilities, correctional institutions, and nursing homes 2
The second test should be administered 1-3 weeks after the first test if the initial result is negative or shows a small reaction 2
A second test (booster) response of ≥10 mm indicates past TB infection 2

The Centers for Disease Control and Prevention recommends administering initial PPD tests as soon as possible after exposure to an unrecognized infectious TB case in a facility 3
If the initial test is negative, administer a second test 12 weeks after exposure was terminated 3
Test the most intensely exposed persons first; expand to less exposed individuals only if transmission is documented 3
Persons with previously positive PPD results do not require repeat testing after exposure unless they develop symptoms suggestive of TB 3