Laboratory diagnosis of acute myocardial infarct: usefulness of determination of lactate dehydrogenase (LDH)-1 level and of ratio of LDH-1 to total LDH.

Recent development of an antibody to the M subunit of lactic dehydrogenase (LDH) allows the rapid isolation and measurement of LDH-1 levels. I and my colleagues studied 101 consecutive patients admitted to the hospital for possible acute myocardial infarct (AMI). The LDH-1 level was 100 IU/L or more, and the ratio of LDH-1 to total LDH (LDH-1/LDH-T ratio) was 0.40 or higher, during the course of illness in 93% of the patients with AMI. The specificity was 95% and the positive predictive value, 86%. These two criteria were met eight to 24 hours after the appearance of symptoms, and often persisted seven to 14 days. Measurement of LDH-1 level and LDH-1/LDH-T ratio is a useful adjunct in the laboratory diagnosis of AMI.