[Significance of lactate dehydrogenase levels in the fluid and serum in the diagnosis of pleural effusions].

Lactic acid dehydrogenase (LAD) levels were determined in 82 pleural effusion liquids and the respective blood samples from 58 patients. Effusions were classed as transudates and exudates on the basis of clinical and laboratory data. The 16 transudates had absolute protein levels of less than 3 g/100 ml and a liquid: serum protein ratio below 0.5. LAD values were below 100 mU/ml and the liquid: serum ratio was less than 0.33, whereas both these levels were exceeded in the case of the 66 exudates. The liquid: serum LAD ratio is better suited for the differentiation of transudates and exudates, particularly if it is related to the liquid: serum protein ratio. Neoplastic effusions have the highest absolute LAD values and liquid: serum LAD ratios. Slighter lower values are noted in TB. Taken in conjunction with other parameters, liquid and serum LAD levels enable a transudate to be distinguished from an exudate and assist in aetiological diagnosis.