Detection of heat stable mycobacterial antigen in cerebrospinal fluid by Dot-Immunobinding assay

Isolation of Mycobacterium tuberculosis in cerebrospinal fluid (CSF) specimen in patients with tuberculous meningitis (TBM) is infrequent and carries low sensitivity. Thus development of an alternative laboratory diagnostic test is essential for the early diagnosis and treatment of TBM.

A simple, rapid Dot immunobinding assay (Dot-Iba), for the laboratory diagnosis of TBM is devised. This method minimizes the risk of handling infectious material in the laboratory.

The Dot-Iba was standardized with heat-inactivated M tuberculosis antigen (PPD). The heat-inactivated CSF from TBM and non-TBM patients was similarly assayed and it can detect antigen upto 1ng/ml in CSF.

A positive result was obtained in all the five culture positive patients with TBM and in 20/25 probable TBM. A negative result was obtained in 38/40 CSF from disease control group. The overall sensitivity and specificity of Dot-Iba was 83.3% and 95% respectively.

Dot-Iba can be used as an adjunct for the laboratory diagnosis of TBM, particularly in culture negative TBM patients and also in those clinical situations where no laboratory tests are available to distinguish between TBM and partially treated pyogenic meningitis.