This review describes the usefulness of monitoring the activity level of lactate dehydrogenase (LDH) and its isoenzyme pattern as indicators of pathological conditions in the lungs, such as cell damage or inflammation. Cytoplasmatic cellular enzymes, like LDH, in the extracellular space, although of no further metabolic function in this space, are still of benefit because they serve as indicators suggestive of disturbances of the cellular integrity induced by pathological conditions. Since LDH is an enzyme present in essentially all major organ systems, serum LDH activity is abnormal in a large number of disorders. Although the increase in total serum LDH activity is rather nonspecific, it is proposed that measurement of LDH activity levels and its isoenzyme pattern in pleural effusion and, more recently, in bronchoalveolar lavage fluid may provide additional information about lung and pulmonary endothelial cell injury.
