Cerebrospinal fluid adenosine deaminase for the diagnosis of tuberculous meningitis

Background: A consensus on the diagnostic utility of cerebrospinal fluid adenosine deaminase (ADA) for tuberculous meningitis (TBM) is lacking. Methods: Patients aged ≥12 years admitted with CNS infections were enrolled prospectively. ADA was measured with spectrophotometry. Results: We enrolled 251 TBM and 131 other CNS infections. The optimal cutoff of ADA was calculated at 5.5 U/l against microbiological reference standard with area under curve 0.743, sensitivity 80.7%, specificity 60.3%, positive likelihood ratio 2.03 and negative likelihood ratio 3.12. The widely used cutoff value 10 U/l had specificity 82% and sensitivity 50%. The discriminating power was higher for TBM versus viral meningoencephalitis than bacterial or cryptococcal meningitis. Conclusion: Cerebrospinal fluid ADA has a low-to-modest diagnostic utility.