Adenosine Deaminase Activity in the CSF of Patients with Aseptic Meningitis: Utility in the Diagnosis of Tuberculous Meningitis or Neurobrucellosis

We assayed 229 CSF samples from 180 adults with meningitis of different etiologies for adenosine deaminase activity (ADA) and evaluated the usefulness of this assay in the differential diagnosis of aseptic meningitis. Cases of meningitis were classified as tuberculous meningitis (TBM), pyogenic meningitis, viral meningitis, self-resolving aseptic meningitis without a specific diagnosis, meningitis associated with other infections, and neoplastic meningitis. We also tested 117 CSF specimens for which parameters were normal. We chose a cutoff point of 10 IU/L on the basis of our results and found elevated ADA levels in 50% of the patients with TBM (no differences between patients with AIDS and those who did not have AIDS were observed). Among samples from patients with aseptic meningitis, we observed high ADA levels in only two of five of the patients with neurobrucellosis. Therefore, we concluded that in cases of aseptic meningitis, a CSF ADA level of > or = 10 IU/L has a sensitivity of 48%, a specificity of 100%, a positive predictive value of 1, and a negative predictive value of 0.91 as a diagnostic criterion for TBM or neurobrucellosis. ADA levels were also > 10 IU/L in 30% of the patients with pyogenic meningitis, but this diagnosis was easily excluded on other grounds.