Reverse passive haemagglutination (RPHA) test for detection of mycobacterial antigen in the cerebrospinal fluid for diagnosis of tubercular meningitis.

BACKGROUND

Various serological techniques have been developed to detect antibodies and antigens in the cerebrospinal fluid (CSF) for diagnosis of tubercular meningitis. Most of the serological assays are ELISA based. Attempts have been made to use much simpler antigen detection techniques like the reverse passive haemagglutination (RPHA)which is simple and cost-effective.

AIMS

To evaluate the reverse passive haemagglutination (RPHA) test for detection of mycobacterial antigens in the CSF for diagnosis of tubercular meningitis.

METHODS

In the present study, we have made the use of polyclonal antiserum against heat killed whole Mycobacterium tuberculosis bacilli to sensitize the RBCs in RPHA to detect antigens in clinically suspected cases. A total of 46 cases (clinically suspected TBM 24, culture proven TBM 2, non- TBM cases 20) were included in the present study for detecting M. tuberculosis antigen in the CSF specimens.

RESULTS

Of the 26 test CSF specimens, 13 CSF specimens were positive by RPHA while 4 of the 20 control CSF specimens were also reactive. Two culture positive specimens included in the study were positive by RPHA. Of the 4 control CSF specimens positive by RPHA, 3 were culture proven cases of pneumococcal meningitis and 1 was a case of cryptococcal meningitis. The RPHA is found to be 50% sensitive and 80% specific; and showed a 76.4 % positive predictive value and a 55.2 % negative predictive value.

CONCLUSION

The RPHA is a simple test that could be used as an adjunct in diagnosing TBM. It does not require any special equipment or technically trained or skilled manpower. It is economical and can be afforded for use in community where TBM is more prevalent. Even though the present study showed a poor sensitivity and specificity, further identification, characterization and evaluation of better immuno-dominant and specific antigens or epitopes, and the usage of antibodies developed against such mycobacterial antigens might improve the sensitivity and specificity of this test.