The use of adenosine deaminase and interferon-γ as diagnostic tools for tuberculous pericarditis
Background: Traditional diagnostic tests for pericardial tuberculosis (TB) are insensitive and often require long culture periods, and this has led to more emphasis being placed on biochemical tests such as the pericardial adenosine deaminase (ADA) test. However, controversy exists as to its diagnostic utility. In addition, the use of interferon (IFN)-γ, which is a reliable indicator of pleural and peritoneal TB, has not been explored in pericardial effusions. We investigated ADA and IFN-γ levels in pericardial effusions of different etiologies. Methods and results: A prospective study was carried out from February 1995 to February 1998 at Tygerberg Hospital (South Africa), with pericardial taps being performed under echocardiographic guidance. During this period, 110 consecutive patients presenting with large pericardial effusions were included in the study. Diagnoses were made according to predetermined criteria, and they included TB (n = 64), malignancy (n = 12), nontuberculous infections (n = 5), other effusions (n = 19), and effusions of uncertain origin (n = 10). The median ADA level in the tuberculous group was 71.7 U/L (range, 10.3 to 303.6 U/L), which was significantly higher than that in any other group (p < 0.05). With a cutoff level for ADA activity of 30 U/L, sensitivity was 94%, specificity was 68%, and positive predictive value was 80%. IFN-γ levels were determined in 30 subjects. The median IFN-γ concentration in the tuberculous group was > 1,000 pg/L, which was significantly higher than in any other diagnostic group (p < 0.0005). A cutoff value of 200 pg/L for IFN-γ resulted in a sensitivity and specificity of 100% for the diagnosis of pericardial TB. Conclusion: Pericardial fluid levels of ADA and IFN-γ are useful in the diagnosis of tuberculous pericarditis.