The diagnostic utility of adenosine deaminase isoenzymes in tuberculous pleural effusions.

SETTING

Pleural adenosine deaminase (ADA) levels have been found to be useful in diagnosing tuberculous pleuritis. Elevated ADA levels have been attributed to ADA2 isoenzyme, although no comprehensive studies have evaluated ADA2 as a diagnostic test.

OBJECTIVE

To estimate the diagnostic accuracy of ADA and ADA2 in diagnosing tuberculous pleurisy.

METHOD: A 3-year retrospective study was carried out. ADA and ADA2 were determined on patients diagnosed according to predetermined criteria.

RESULTS

A total of 951 samples were received, including 387 patients with tuberculosis (TB). ADA values>or=52.4 U/l yielded a sensitivity, specificity and positive (PPV) and negative predictive value (NPV) respectively of 93.7% (95%CI 90.0-96.0), 88.7% (95%CI 85.7-91.3), 85.5% (95%CI 81.7-88.8) and 95.2% (95%CI 92.9-96.9). ADA2 values>or=40.6 U/l yielded a sensitivity, specificity and PPV and NPV of respectively 97.2% (95%CI 95.0-98.7), 94.2% (95%CI 91.8-96.0), 92.2% (95%CI 89.1-94.7) and 98.0% (95%CI 96.3-99.0). The chi2 and McNemar tests proved the superiority of ADA2 statistically.

CONCLUSION

ADA2 is superior to ADA in the diagnosis of tuberculous pleuritis and should be used as a routine test in the diagnostic work-up of patients with pleural effusions in areas with high TB prevalence.