The possible role of cerebrospinal fluid adenosine deaminase activity in the diagnosis of tuberculous meningitis in adults

We studied an adenosine deaminase (ADA) activity in the cerebrospinal fluid (CSF) of 182 patients with meningitis. The patients were subdivided into four groups, (1) 36 cases of tuberculous meningitis; (2) 130 cases of viral or aseptic meningitis; (3) nine cases of bacterial meningitis; (4) seven cases of cryptococcal meningitis. Mean±S.D. ADA activity was 12.76±7.53 U/l in group 1; 2.58±2.37 U/l in group 2; 7.38±3.27 U/l in group 3; 7.42±4.38 U/l in group 4. Comparing the ADA activity in each group with the other groups, the difference is significant (P<0.001), except between groups 3 and 4. The sensitivity of the test for group 1 compared with group 2 was 0.83 and the specificity was 0.95 when a cut-off value of 7 U/l was used. When group 1 was compared with groups 3 and 4, the sensitivity was 0.58 and the specificity was 0.89 and 0.71 with groups 3 and 4, respectively, when a cut-off value of 10 U/l was used. Values >15 U/l were not observed in any of the non-tuberculous meningitis patients; therefore, ADA activity >15 U/l could be a strong indication of tuberculous meningitis. We conclude that a determination of CSF ADA can aid in the early differential diagnosis of tuberculous meningitis.