Sensitivity and specificity of the FLA-ABS test for leprosy in Mexican populations.

The epidemiological surveillance for leprosy must include several clinical and laboratory procedures. The FLA-ABS test of Abe could be a useful tool for this purpose because it allows the demonstration of an effective contact with Mycobacterium leprae. In order to establish the specificity, sensitivity, and predictability of the FLA-ABS test under Mexican conditions, we studied sera collected from six groups of individuals: 60 healthy donors from a nonendemic area, 57 cases hospitalized for conditions other than infectious diseases from a general hospital in a nonendemic area, 72 patients with active pulmonary tuberculosis, 26 healthy individuals from an endemic area, 100 patients with polar lepromatous leprosy (LLp), and 123 household contacts of patients with LLp. The FLA-ABS test was negative with sera from the first four groups. Strong positive reactions were found in all LLp patients except one; the false-negative results could be attributed to successful treatment and a long-standing cure in this patient. Analysis of these results shows 100% specificity, 99% sensitivity, and predictability values of the test of 100% for positive results and 99% for negative ones. In addition, none of the 20 randomly selected sera from LLp patients were positive with crossreacting mycobacteria. Because 87.8% of the household contacts were positive in the absence of clinical manifestations of leprosy, it is possible to conclude that a positive result by itself is not enough to establish an early diagnosis of the disease, especially among inhabitants of endemic areas.(ABSTRACT TRUNCATED AT 250 WORDS)