Assay of Cardiac Lactate Dehydrogenase Iso‐enzymes by Means of Urea

Abstract

The determination of serum lactate dehydrogenase (LDH) has been used as a diagnostic test of myocardial infarction since 1955 (22). The electrophoretic fractionation of LDH into iso-enzymes and the observation that each tissue has a characteristic iso-enzyme pattern (16,19) has increased the accuracy in diagnosing the origin of the enzymes released into the serum. Electrophoresis with subsequent staining of the five iso-enzymes is, however, a cumbersome and time-consuming procedure for routine use in clinical laboratories. T o avoid this disadvantage efforts have been made to develop simplified tests specific for LDH iso-enzymes of cardiac muscle. Inactivation of LDH,-6 iso-enzymes (the main iso-enzymes of liver and skeletal muscle) by heat (3,15,21,23), acetone ( lo), and chloroform ( 1 7) has been applied for this purpose. The use of a-ketobutyrate as substrate (4, 7, 8,13,14), instead of pyruvate, favours the detection of cardiac iso-enzymes