Selection of skin test antigens to evaluate PPD anergy

A purified protein derivative (PPD) tuberculin skin test may be nonreactive because of cutaneous anergy, technical problems with the test, or absence of tuberculosis infection. This study investigated the sensitivity and specificity of five test agents in measuring cutaneous anergy when the PPD test is nonreactive. Agents evaluated include antigens for Candida, mumps, histoplasmin, tetanus, and Trichophyton.

Delayed-type hypersensitivity skin test records were analyzed in 1113 patients admitted to the University of Texas Health Center at Tyler from December 1988 through June 1993. These patients were admitted with initial diagnoses of diseases other than active tuberculosis or human immunodeficiency virus infection.

Patients with a negative PPD test reacted most often to the control skin test Candida (63.5%), followed by mumps (52.2%), histoplasmosis (37.2%), tetanus (35.7%), and Trichophyton (6.1%). Analysis of these data indicates that the use of more than three of the four most commonly reactive control tests (Candida, mumps, and histoplasmin or tetanus) yielded minimal additional precision in the determination of skin test anergy compared with using all five control skin tests. This finding remained constant whether the PPD was considered negative at < 5 mm, < 10 mm, or < 15 mm of induration.

In controlling for false-negative PPD tests, the use of three skin test antigens, Candida, mumps, and tetanus, should provide reliable control for delayed-type hypersensitivity anergy.