Lactic dehydrogenase isoenzyme determination in the diagnosis of acute myocardial infarction.

Lactic dehydrogenase (LD) isoenzymes were determined by a rapid, simple technique and their utility in the diagnosis of acute myocardial infarction (AMI) was evaluated. LD isoenzymes were separated by ion-exchange column chromatography using DEAE-Sephadex. The cardiac fractions (LD-1 and LD-2) were measured separately on an Abbott ABA-100 analyzer and ratio of LD isoenzyme 1 to LD isoenzyme 2 (LD1:2) calculated. Daily serum samples were obtained from 100 patients selected only for a history of chest pain of abrupt onset. In 47 patients whose diagnosis was acute myocardial infarction (AMI), confirmed by typical clinical presentation and typical rise in cardiac-specific creatine kinase isoenzyme (MB(, peak LD1:2 ranged from 0.77 to 2.26. In 44 patients without AMI, peak LD1:2 ranged from 0.25 to 0.76. In two patients with electrocardiographic changes chest pain occurred two and five days previously; there was no rise in MB, but LD1:2 was elevated. Four patients with small AMI had no rise in LD1:2. Three more patients (one with active hemolysis) had false positive results. Thus, there was a sensitivity of 96% and a specificity of 97% when the cut-off point was LD1:2 = 0.76. LD1:2 is not quite as sensitive or specific as MD, but the ratio allows for the diagnosis of infarction in cases where MB has already returned to normal.