Role of cerebrospinal fluid adenosine deaminase level estimation in diagnosis of tuberculous meningitis.

Five lakh patients of tuberculosis die every year in India. Meningeal tuberculosis is an endemic disease with 7-12% incidence. Delay in diagnosis and in initiating treatment results in poor prognosis and sequelae in upto 25% of cases. The aim of the present study is to look for a simple, rapid, cost effective and non-invasive test for diagnosing this disease. Forty patients between 6-24 months of age having symptoms and signs of meningitis were selected and divided into two groups tuberculous and non-tuberculous, depending upon the accepted criteria. Cerebrospinal fluid (CSF) was drawn and adenosine deaminase (ADA) estimated. Out of 19 tuberculous patients, 18 patients had CSF ADA at or above the cut-off value while 1 had below the cut-off value. Out of 21 non-tuberculous patients, 2 patients had at or above the cut-off value while 19 were below this value. Results of this study indicate that ADA level estimation in CSF is not only of considerable value in the diagnosis of tuberculous meningitis, CSF ADA level of 10 U/L as a cut-off value exhibited 94.73% sensitivity and 90.47% specificity in differentiating tuberculous from non-tuberculous meningitis; it also has 90.00% positive predictive value and 95.00% negative predictive value. ADA estimation in CSF is simple, inexpensive, rapid and fairly specific method for making a diagnosis of tuberculous aetiology in TBM; especially when there is a dilemma of differentiating the tuberculous aetiology from non-tuberculous and for this reason ADA estimation in TBM may find a place as a routine investigation.