A case of tuberculous pleural effusion with low pleural fluid adenosine deaminase levels

Traditionally, Mycobacterium tuberculosis or granulomas have to be evidenced in the pleural cavity in order to establish a diagnosis of tuberculous pleuritis. In recent years, adenosine deaminase has aided tremendously in the diagnosis of tuberculous pleural effusion, often obviating the need for microbiologic or histologic verification of the diagnosis. However, the fact that the sensitivity of pleural fluid adenosine deaminase levels for tuberculous pleurisy, although high, is incomplete is often overlooked. To emphasize this, we present a case of a young male adult who presented with fever and a right-sided exudative bloody lymphocytic pleural effusion. While pleural fluid adenosine deaminase levels were low (22 U/L) and all other tests were inconclusive, tuberculin skin test conversion within the first two weeks of observation provided the clue for a clinical diagnosis of tuberculous pleurisy. The patient responded promptly to a four-drug regimen including isoniazide, rifampin, ethambutol, and pyrazinamide and had a normal chest X-ray at one month post-therapy initiation. He is well after two years of follow-up. Not all patients with a tuberculous pleuritis will have elevated adenosine deaminase levels in pleural fluid, and low pleural fluid adenosine deaminase levels do not rule out tuberculous pleuritis, especially in areas of high tuberculosis incidence.