Evaluation of Adenosine Deaminase Activity in Cerebrospinal Fluid: A Comparison Between Tuberculous and Non-Tuberculous Meningitis

Abstract

Background: Tuberculous central nervous system (CNS) infection is the most severe form of tuberculosis (TB). Tuberculous meningitis (TBM) is the commonest form of CNS TB caused by Mycobacterium tuberculosis bacilli and the diagnosis of TBM is often difficult. A cost-effective, reliable and rapid diagnostic test, which can be performed in any equipped laboratory, could be of help in the diagnosis of TBM. In the present study, we measured the adenosine deaminase (ADA) activity in cerebrospinal fluid (CSF) of TBM and non-TBM patients.

Objective: To find out the diagnostic value of CSF ADA in the diagnosis of TBM by measuring the sensitivity and specificity of CSF ADA and comparing the CSF ADA level between TBM and non-TBM patients.

Method: This cross-sectional observational study was done in the Neurology Department of BSMMU, Dhaka. ADA activity in the CSF of both TBM and non-TBM patients was estimated according to a method based on the DiazymeR commercial kit’s manual using a semi-automated biochemistry analyzer. Comparison was done between the CSF ADA levels of TBM and non-TBM patients. The sample size was 80. The sampling method was purposive and included both sexes and all age groups. Diagnosis of TBM and non-TBM meningitis was based on appropriate diagnostic criteria.

Results: The mean CSF ADA activity was found to be significantly higher in CSF of TBM patients, 12.9 ± 9.2 U/L (6.2-39.0 U/L), mean ± SD with range, than in the CSF of non-TBM meningitis patients, 5.1± 3.0 U/L (2.7-20.7 U/L); p value was <0.001. A cutoff value of 9.3 U/L was used to differentiate TBM from non-TBM. The sensitivity and specificity of CSF ADA were 76.9% and 77.6% respectively, for the diagnosis of TBM when this cutoff value was used.

Conclusion: This study demonstrated that the estimation of ADA level in CSF of TBM patients, using a cutoff value 9.3 U/L, may be useful for early diagnosis of TBM in our country, as this test can be performed in any equipped laboratory where more sophisticated methods are not available.