The pleural-fluid-to-serum-albumin ratio was also evaluated, but there was more overlap between exudates and transudates (data not shown). Lights criteria correctly identified all 41 patients with exudates; however, five patients with a transudative cause for their pleural effusion were misclassified as exudates using Light’s criteria. One patient had a high protein ratio (0.52), two patients had high LDH ratios (0.85; 0.68), one patient had an LDH level greater than 200 U/L, with a high LDH ratio (245 U/L and 0.73), and one patient had both a high protein ratio and high LDH ratio (0.57 and 0.84). Using an albumin gradient of greater than 1.2 g/dl to indicate a transudate, all of these patients were correctly classified as having transudates (albumin gradients of 1.4, 2.2, 1.6, 1.6, and 1.3 g/dl).
All five of these patients had clinical congestive heart failure, and all five had a response to diuretic therapy with a decrease in the pleural effusion. Four of the patients had chronic congestive heart failure that had been treated with diuretics before the thoracentesis. One of the patients with a left-sided effusion had a pleural biopsy because of a history of a skin test positive to tuberculosis. This was negative, and the effusion resolved with increased diuretic therapy. The other four patients had bilateral eflusions, and further diagnostic evaluation was not done due to the improvement or resolution of the effusion with diuretic therapy.