Kinetic Determination of Cerebrospinal Fluid Adenosine Deaminase Activity for the Diagnosis of Tuberculous Meningitis

Tuberculous meningitis (TBM) is a common infectious disease of the central nervous system. Detection of cerebrospinal fluid (CSF) adenosine deaminase (ADA) activity for the diagnosis of TBM has a relatively high accuracy. Most previous reports determined ADA levels by following the colorimetric method of Giusti (endpoint assay). Recently, a Diazyme ADA assay kit was developed to determine CSF ADA levels. This study aimed to define the cutoff value of CSF ADA that is diagnostic for TBM with the Diazyme ADA assay kit. Adults with meningitis were included in the study. The diagnostic properties of CSF ADA for TBM as determined by the Diazyme ADA assay kit were assessed by the receiver operating characteristic curve, area under the curve, sensitivity, specificity, and likelihood ratios. There were 97 patients enrolled in the study, comprising 15 cases of TBM and 82 cases of non-TBM meningitis. The median CSF ADA activity level in the TBM group was significantly higher than in the non-TBM group (P = 0.002), with a mean difference of 14.5 U/L (95% CI: 5.3-23.8 U/L). A CSF ADA level of 6.1 U/L was the best cutoff value to differentiate between the TBM and non-TBM groups, with a sensitivity of 53.33%, a specificity of 89.02%, a positive likelihood ratio of 4.86, a negative likelihood ratio of 0.52, and an area under the curve of 0.75. A CSF ADA level of 6.1 U/L determined by the Diazyme ADA assay kit could be used as a diagnostic tool in the early diagnosis of TBM.