Adenosine Deaminase Levels in CSF of Tuberculous Meningitis Patients

BACKGROUND: Tuberculosis kills five lakh patients in India every year, out of which 7-12 % are with meningeal involvement. Delay in its diagnosis and in initiation of treatment results in poor prognosis and sequlae in up to 25% of cases. The aim of the present study is to look for a simple, rapid, cost effective, non-invasive and fairly specific test in differentiating tubercular etiology from other causes. METHODS: Forty patients between the age of 6 - 24 months attending hospital with symptoms and signs of meningitis were selected and divided into two groups: tubercular and non-tubercular, depending upon the accepted criteria. CSF was drawn and ADA estimated. RESULTS: Out of 19 tubercular patients, 18 had CSF ADA at or above the cutoff value while one had below. Out of 21 non-tuberculous patients, two had ADA levels at or above the cutoff value while 19 had below this value. Results of our study indicate that ADA level estimation in CSF is not only of considerable value in the diagnosis of TBM, CSF ADA level 10 U/L as a cutoff 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. CONCLUSIONS: It can be concluded that ADA estimation in CSF is not only simple, inexpensive and rapid but also fairly specific method for making a diagnosis of tuberculous etiology in TBM, especially when there is a dilemma of differentiating the tuberculous etiology from non-tuberculous ones. For this reason ADA estimation in TBM may find a place as a routine investigation. KEYWORDS: Cerebrospinal fluid; Adenosine deaminase; Tuberculous meningitis