Evaluation of Adenosine Deaminase as a Diagnostic Marker in Tuberculous Pleural Effusion

Tuberculous pleural effusion (TPE) is a common medical condition more frequently encountered in poor countries. It is the second most common form of extra-pulmonary tuberculosis. The diagnosis of TPE is problematic because the clinical features are non-specific, and most laboratory tests are not diagnostic. An accurate diagnosis requires the detection of TB bacilli in the pleural fluid or tissue sample from the pleura, which is not an easy task due to the scarcity of bacilli in the pleural fluid and the need for invasive maneuvers to get pleural tissue for histopathological, bacteriological or molecular confirmation for the TB bacilli. Different markers in pleural fluid have been evaluated to aid in diagnosing TPE. Among those biomarkers, Adenosine deaminase (ADA) was the most studied marker. It is an enzyme predominantly produced by T-lymphocytes and catalyzes the conversion of adenosine to inosine and deoxyadenosine. It is a hallmark of active cellular immunity. A high level of ADA can be found in exudative effusion of different etiologies such as parapneumonic, tuberculous and malignant effusions. Although there is still a debate over the diagnostic accuracy of ADA as a marker for TPE, many studies recommend its use. A correct diagnosis is crucial for the start of treatment for TPE. Therefore, it is crucial to assess the diagnostic value of adenosine deaminase in diagnosing tuberculous pleural effusion. The ADA optimal cutoff value is still under investigation.