A 5-year-old girl is referred to your clinic for evaluation of her tuberculin skin test. She had a Mantoux test containing 5 tuberculin units of purified protein derivative placed intradermally 48 hours ago. Evaluation of the test demonstrates 18 mm of induration. She moved to the United States 3 years ago and was immunized with bacillus Calmette-Guérin (BCG) vaccine at birth. Findings on chest radiography are negative.


The recommended time for assessing the TST is 48 to 72 hours after administration. The area of induration (not erythema) should be measured using the ballpoint pen technique and recorded in millimeters. A negative TST result never excludes the diagnosis of tuberculosis.

Any child who has a positive tuberculin skin test (TST) of greater than 15 mm induration should be considered to be infected with Mycobacterium tuberculosis.

Results should be considered positive if there is more than 5 mm of induration in the following situations:

Positive results are associated with more than 10 mm of induration in the following situations:

Positive results are associated with more than 15 mm of induration in the following situations:


The BCG Vaccine

Live vaccine from M. bovis

PPD and BCG. Reactivity of the TST after receipt of the bacillus Calmette-Guérin (BCG) vaccine depends the following factors (below).  In general, TST results in individuals who have received BCG should be interpreted similarly to those who have not received BCG. Therefore, a positive test result should not be considered a false-positive

Abernathy RS. Tuberculosis: an update. Pediatr Rev. 1997;18:50-58
Full text is available online for subscription or fee.

American Academy of Pediatrics Committee on Infectious Diseases. Active immunization. In: Pickering LK, ed. Red Book: 2003 Report of the Committee on Infectious Diseases. 26th ed. Elk Grove Village, Ill: American Academy of Pediatrics; 2003:7-53