Utility of dual skin tests to evaluate tuberculin skin test reactions of 10 to 14 mm in healthcare workers.

OBJECTIVE: To define the utility of 10- to 14-mm reactions to a Mycobacterium tuberculosis purified protein derivative (PPD) skin test for healthcare workers (HCWs).

DESIGN: Blinded dual skin testing, using PPD and M. avium sensitin, of HCWs at a single medical center who had a 10- to 14-mm reaction to PPD when tested by personnel from the Occupational Health Department as part of routine annual screening.

SETTING: A single tertiary-care academic medical center.

PARTICIPANTS: Employees of the medical center who underwent routine annual PPD screening and were identified by the Occupational Health Department as having a reaction of 10 to 14 mm to PPD.

RESULTS: Nineteen employees were identified as candidates and 11 underwent dual skin testing. Only 4 (36%) had repeat results for PPD in the 10- to 14-mm range, whether read by Occupational Health Department personnel or study investigators. For only 5 (45%) of the subjects did the Occupational Health Department personnel and study investigators concur (+/- 3 mm) on the size of the PPD reaction. Two of the 4 subjects with reactions of 10 to 14 mm as measured by the study investigators were M. avium sensitin dominant, 1 was PPD dominant, and 1 was nondominant.

CONCLUSION: A reaction of 10 to 14 mm to PPD should not be used as an indication for the treatment of latent tuberculosis (TB) infection in healthy HCWs born in the United States with no known exposure to TB.