Cerebrospinal fluid adenosine deaminase and lysozyme levels in the diagnosis of tuberculous meningitis

Adenosine Deaminase Activity (ADA) and Lysozyme Activity (LYSA) were measured in the CSF of tuberculous meningitis (TBM) cases : 26 bacteriologically positive TBM (Group 1), 61 bacteriologically negative TBM (Group 2), 10 non-tuberculous meningitis (Group 3) and 17 control subjects (Group 4). The mean ADA levels in different groups in that order were found to be 11.6, 4.5, 4.4 and 0.8 U/l respectively. The mean LYSA levels in the same groups were 6.3, 2.1, 2.2 and 0.5 mcg/ml respectively. In bacteriologically positive TBM, the mean ADA and LYSA levels were significantly higher than the other three groups (p < 0.0001). An ADA level of 4U/l and LYSA tests were 96%, 82% and 85%, 95% respectively. When both the criteria were considered, the sensitivity and specificity were 91% and 93% respectively. Combination of both test definitions could give additional support to the diagnosis in 49% of 61 clinically suspected but bacteriologically negative TBM cases. Correlation of ADA and LYSA levels in CSF was found to be statistically significant (r = 0.59; p < 0.01)