Useful tests on pleural fluid that distinguish transudates from exudates

We aimed to compare the classic Light's criteria with different testing str ategies in an effort to improve the accuracy of pleural fluid (PF) categori zation. Thirty-two patients with transudates and 140 with exudates con the basis of their clinical diagnosis were entered into the study. We examined the discriminative properties of 10 analytes in the identification of PF, b oth singly and in combination with an 'or' rule, to see which was best in d istinguishing a transudate from an exudate. A combination of PF lactate deh ydrogenase (LD) > 307 U/L (two-thirds of the upper limit of the serum LD re ference range) with either PF cholesterol > 1.55 mmol/L or PF to serum prot ein ratio > 0.5 had a diagnostic accuracy similar to that of Light's criter ia. We suggest the use of PF LD and cholesterol in combination as an altern ative method for distinguishing pleural transudates from exudates. This tes t combination avoids the need for venepuncture and the simultaneous collect ion of a blood sample.