Comparative analysis of cerebrospinal fluid adenosine deaminase activity in meningitis

The purpose is to determine the cut-off value of adenosine deaminase (ADA) activity in cerebrospinal fluid (CSF) of patients with tuberculous and non-tuberculous meningitis, and to assess its value in differential diagnosis.

This study was conducted in 91 patients with meningitis in two university hospitals in Turkey. 24 patients had tuberculous meningitis (TBM), 25 purulent meningitis (PM), 25 aseptic meningitis (AM) and 17 neurobrucellosis (BM). ADA activity of CSF was quantified by colorimetry.

In our study, mean ADA values in CSF were 28.34 ± 14.83 IU/L in TB cases, 8.71 ± 5.83 IU/L in BM, 6.18 ± 2.54 IU/L in PM and 3.43 ± 3.48 U/L in AM cases. If we accept for CSF ADA an activity cut-off value of 12.5 IU/L for differential diagnosis of TBM and BM, its sensitivity was 92% and specificity was 88%. If we accept 12.35 IU/L for differential diagnosis of TBM and PM, its sensitivity was 92% and specificity was 100%. If we accept 6.45 IU/L for differential diagnosis of TBM and AM, its sensitivity was 100% and specificity was 92%. Additionally, we examined the cases after dividing them into two groups, viz. TB and non-TB. If we accept an ADA activity cut-off level of 11 IU/L for differential diagnosis of TB and non-TB by applying ROC analysis, its sensitivity was 92% and specificity was 90%.

The sensitivity and specificity for CSF ADA activity are markedly high in differential diagnosis of TB from non-TB. Hence CSF ADA activity may be used as a simple, cost-effective and reliable test for early differential diagnosis of TB.