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 differen t etiologies for adenosine deaminase activity (ADA) and evaluated the usefulness of this assay in the differential diagnosis of aseptic meni ngitis. Cases of meningitis were classified as tuberculous meningitis (TBM), pyogenic meningitis, viral meningitis, self-resolving aseptic m eningitis without a specific diagnosis, meningitis associated with oth er infections, and neoplastic meningitis. We also tested 117 CSF speci mens for which parameters were normal. We chose a cutoff point of 10 I U/L on the basis of our results and found elevated ADA levels in 50% o f the patients with TBM (no differences between patients with AIDS and those who did not have AIDS were observed). Among samples from patien ts with aseptic meningitis, we observed high ADA levels in only two of five of the patients with neurobrucellosis. Therefore, we concluded t hat in cases of aseptic meningitis, a CSF ADA level of greater than or equal to 10 IU/L has a sensitivity of 48%, a specificity of 100%, a p ositive predictive value of 1, and a negative predictive value of 0.91 as a diagnostic criterion for TBM or neurobrucellosis. ADA levels wer e also >10 IU/L in 30% of the patients with pyogenic meningitis, but t his diagnosis was easily excluded on other grounds.