Detection of Mycobacterium tuberculosis antigen 5 in cerebrospinal fluid by inhibition ELISA and its diagnostic potential in tuberculous meningitis.

Inhibition ELISA was used to quantitate Mycobacterium tuberculosis antigen 5 in cerebrospinal fluid (CSF) specimens of 40 patients with a clinical diagnosis of tuberculous meningitis. In all 10 culture-proven patients, the assay was positive; in 30 culture-negative patients, the assay yielded positive results for 21. CSF antigen 5 concentrations ranged from 9 to 82 ng/ml (mean +/- SD, 45.5 +/- 6.2). In 40 patients with nontuberculous neurologic diseases, mean concentration was 1.45 ng/ml. Thus, inhibition ELISA for the detection of M. tuberculosis antigen 5 in CSF has definite diagnostic potential during the active phase of the disease and should be a routine diagnostic test, particularly when bacteriologic cultures in CSF are negative for M. tuberculosis.