Apparent false positive histoplasmin latex agglutination tests in patients with tuberculosis

Serum specimens from patients admitted to a respiratory disease hospital were examined by the histoplasmin latex agglutination, the complement fixation, and the agar gel immunodiffusion tests. Of 300 sera examined, 21 (7.0%) gave an apparent false positive reaction at a dilution of 1:16 or greater. Fourteen (66%) of the 21 patients studied has culturally proven tuberculosis. One patient each had a diagnosis of hypertensive cardiovascular disease with congestive heart failure, infection with atypical mycobacteria (Runyon group III), chronic pneumonitis secondary to gunshot wound, and pulmonary abscess of unknown etiology; two had bronchogenic carcinoma; and one serum specimen came from an apparently healthy employee. The results of the histoplasmin latex agglutination test should be interpreted with caution, particularly if only one serological determination has been made and the titer is low.