False-positive reactions with enzyme-linked immunosorbent assay of Mycobacterium tuberculosis antigens in pleural fluid.

The value of enzyme-linked immunosorbent assay (ELISA) for the diagnosis of tuberculous pleural effusion has not been defined. We performed ELISA by a double antibody sandwich technique with anti-BCG antibody in the solid phase to detect Mycobacterium tuberculosis antigen in pleural fluid from 36 patients with pleural effusion (tuberculosis 15, lung cancer 12, miscellaneous 9). Pleural fluids from 12 of the tuberculosis patients, 12 of the cancer patients and one patient in the miscellaneous group had optical densities above the cut-off point. False-positive reactions in patients with lung cancer limit the usefulness of ELISA with conventional anti-BCG antibody for detection of M. tuberculosis antigen.