Comparative analysis of cerebrospinal fluid adenosine deaminase in tuberculous and non-tuberculous meningitis.

OBJECTIVE: To calculate cut-off point for the adenosine deaminase (ADA) activity in the CSF of patients with tuberculous meningitis (TBM).

PATIENTS AND METHODS: The ADA assay was based on the automatic indirect method in which ADA catalyzes adenosine to inosine. ADA activity in the CSF was calculated based on ammonia liberated from adenosine and quantified spectrophotometrically. Arithmetic mean values and standard deviation of each variable were measured. Mann-Whitney U and Fisher exact tests were applied to compare continuous and dichotomous variables between tuberculous and non-tuberculous groups. A receiver operating characteristic curve was plotted to identify various cut-off points to determine the best level for ADA activity.

RESULTS: Totally 42 patients were enrolled into the study. The median of ADA activity in the TBM group was 22 and in the non-TBM group was 8.0. The mean CSF-ADA activity was found to be significantly higher in TBM group (23.05+/-13.1IU/L) than in the CSF from non-TBM patients (9.39+/-5.18IU/L). The highest accuracy is at the cut-off value of 10.5IU/L. The sensitivity and specificity of the test at this cut-off to differentiate TBM from non-tuberculous meningitis is 81% and 86% respectively.

CONCLUSION: Considering that a high positive value of ADA activity cannot confirm TBM, however, in suspected patients it may lead the physician to treat patient earlier before the confirmatory diagnostic reports will be received. The suggested cut-off value in this pilot study is 10.5IU/L with high sensitivity and specificity.