Nevertheless, caution must be observed, given the two cases with malignant cells whose albumin gradient was in the transudative range. Light et al reported one case with malignant cells in the pleural fluid who also had signs and symptoms of congestive heart failure. The criteria of Light et al classified the effusion as a transudate. Patients with mixed causes for ascites (alcoholic hepatic disease and carcinoma) tend to also have a serum-ascites albumin gradient in the transudative range. The two patients in this report may have had mixed causes for their pleural effusions, with the transudative cause being shown by the albumin gradient and the exudative cause being shown by Lights criteria.
In summary, Lights criteria in this series of 59 patients were 100 percent sensitive at identifying exudates; however, these criteria were not as specific (72 percent). The albumin gradient is 100 percent specific and still very sensitive (95 percent). Caution is necessary in cases with possible mixed causes for the eflusion. The serum-effusion albumin gradient is a reliable criterion for differentiating exudates from transudates and can be helpful, especially in cases of congestive heart failure treated with diuretics. More study is necessary to confirm these results.