Serum Adenosine Deaminase Levels in Tubercular Lymphadenitis: Correlation and Cutoff

OBJECTIVES: Tubercular lymphadenitis accounts for the large majority of extrapulmonary tuberculosis (TB) worldwide. The available means for their diagnosis are often time-consuming, tedious, and costly. Adenosine deaminase (ADA) level estimation in body fluids has emerged as a popular method of diagnosing tuberculous infection. Very few studies have examined serum ADA levels in TB lymphadenitis and fewer such studies have used controls. The objective of the present study was to find any correlation between serum ADA and fine-needle aspiration cytology-confirmed tubercular lymphadenitis and, if a correlation existed, whether there existed any diagnostic cutoff for clinical utility.MATERIAL AND METHODS: This prospective study was done over 2 years. The patients were grouped into tubercular lymphadenitis (group 1, cases) and non-tubercular lymphadenitis (group 2, controls). Serum ADA level was estimated using the spectrophotometric method. Statistical methods were employed to examine the intergroup differences in serum ADA levels. The receiver operating characteristic curve (ROC curve) was used to assess the overall accuracy and corresponding diagnostic accuracy at different cutoff values of serum ADA.RESULTS: Tubercular lymphadenitis (Group I) has a strong female predilection (M: F = 0.56:1, P = 0.017), a significantly late clinical presentation (P = 0.002), and a significantly higher incidence of cervical lymph node involvement (P = 0.019). A positive treatment history was significantly and more commonly found in patients of group 1 (P < 0.001) than patients of group 2. The mean serum ADA level was 43.14 IU/L. A significantly higher serum ADA level was detected in group 1 patients than in group 2 (56.81 +/- 12.42 vs. 32.07 +/- 6.84, P < 0.001). On ROC, the area under the curve was 97.2%, indicating a very good discriminating capability of serum ADA levels between groups 1 and 2. A cutoff value of 41.90 IU/L had the best sensitivity and specificity (93.15% and 92.1%, respectively) for detecting a tubercular etiology.CONCLUSION: Serum ADA level of 41.90 U/L can differentiate tubercular from non-tubercular lymphadenitis with a very high sensitivity and specificity. Therefore, serum ADA estimation can facilitate an early clinical diagnosis and institution of treatment.