The Isoenzymes of Lactic Dehydrogenase

Abstract
The DETERMINATION of serum lactic dehydrogenase (LDH) activity is used in the diagnosis of a wide variety of conditions such as myocardial infarction,1pulmonary embolism,2hepatobiliary diseases,3musculoskeletal disorders,4certain neoplasms,5and a variety of hematological diseases.6Hence, to a considerable degree, this enzyme lacks specificity as a diagnostic aid. The separation of LDH into its component isoenzymes represents an attempt to improve its specificity. Lactic dehydrogenase in man consists of five heterogenous isoenzymes. Lactic dehydrogenase 1, the electrophoretically slowest isoenzyme, is present in largest concentration in liver and skeletal muscle, while LDH 5, the electrophoretically fastest isoenzyme, is found in largest concentration in heart muscle and erythrocytes. Lactic dehydrogenase 2, 3, and 4 are distributed widely and in varying amounts in reticuloendothelial, lung, heart, and other tissues.7It has been assumed that serum LDH isoenzyme activity in disease states reflects, at least in part, the isoenzyme activity of tissue

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