Cerebrospinal Fluid Adenosine Deaminase Activity: A Valid Ancillary Test for Tubercular Meningitis

Tuberculosis affects 1.80 million persons every year with 3.70 lakh annual deaths, ˜ 10% of which are of meningeal involvement. Diagnosis of Tubercular meningitis is difficult with often under or over diagnosis. Delay in diagnosis and initiation of treatment results in poor prognosis and sequel in up to 25% of cases. Cerebrospinal fluid (CSF) Adenosine deaminase (ADA) is a simple, reliable, cost effective and rapid diagnostic test that can even be done in small clinical laboratory set up. We evaluated CSF-ADA as an ancillary test for tubercular meningitis (TBM).

Total 118 CSF samples were analyzed in this study under four different groups viz. TBM (n= 30), pyogenic meningitis (PM, n=24), aseptic meningitis (AM, n=20) and Controls (no meningeal involvement, n=44). Diagnosis of meningitis was done by clinicians on the basis of presence of signs of meningeal irritation and cytological and biochemical examination of CSF. CSF-ADA was estimated by method based on Berthelot reaction, which is the formation of a colored indophenol complex from ammonia liberated from adenosine, and quantified colorimetrically. Kruskal-Wallis test with Dunnett's multiple comparison post-test was done to compare CSF-ADA activity in different groups. ROC curve analysis was done for CSF-ADA cutoff value.

Mean CSF-ADA (U/L) value in TBM patients were significantly higher (24.37±10.73) than in PM (14.28±5.979), AM (10.32±5.554) and Controls (6.520±4.801), p-value <0.0001 in TBM vs AM and TBM vs Controls. A cut-off value of 13.3 U/L gave a sensitivity of 91% and specificity of 90% when used to diagnose TBM.

CSF-ADA is not only simple, cost effective and rapid but also fairly sensitive and specific in diagnosis of TBM, especially in dilemma of differentiating the tuberculous etiology from non-infectious one. For these reasons CSF-ADA is a well performer as an ancillary test of TBM.