FALSE-POSITIVE TUBERCULOSIS SKIN-TEST RESULTS

THE RE-EMERGENCE OF tuberculosis as a significant public health threat has led to greatly renewed activity in tuberculin skin testing to ide ntify infected persons. However, even use of the preferred skin test t echnique (intradermal injection of purified pro-rein derivative via th e Mantoux method) can lead to either false positive or false negative results, interpretation of a Mantoux test can be influenced by cross r eactions with other mycobacteria, intertester variation, host-response variation, and product related problems. At least 25 apparent false p ositive purified protein derivative skin test reactions in New York St ate in 1992 appeared to be associated with lots of the derivative prod uced by one manufacturer. These unexpected skin test results led to ex amination of a product with an altered appearance that may have caused the unanticipated responses. After announcement of these false positi ve results to the press, the company removed the product from the mark et. Food and Drug Administration analysis later revealed particulate m atter in vials of the suspected lots of purified protein derivative.