Cellulitis versus positive purified protein derivative? A case report and review of the literature

The tuberculin skin test is one of the most widely used diagnostic aids ever developed and remains the only technique of detecting Mycobacterium tuberculosis infection other than actually culturing the organism. False- positives are an acknowledged problem, especially among health care workers (HCW), in whom rescreening can raise more questions than answers. A HCW presented with a severe response to an annual screening test and was retested 6 weeks later with normal results (non-reactive). Causes of false-positives (not including cross-reactivity) are discussed. Readers of the purified protein derivative reaction need to consider alternative explanations for a significant response than infection with tuberculosis, given the medical history and nature of response.