Lactate dehydrogenase isoenzyme-1: changes during the first day after acute myocardial infarction.

We studied the time course of change of lactate dehydrogenase isoenzyme-1 (LD-1) in serum of patients suspected of having had an acute myocardial infarction. LD-1 was measured at intervals of 4-8 h during the first and second hospital days, by an immunochemical method. Of the 65 patients in this study, 26 had acute myocardial infarctions by traditional criteria. The ratio of LD-1 to total LD had greater diagnostic value than did LD-1 alone. In 90% of patients with myocardial infarction this ratio was increased within 12 h of admission, and all had increased ratios within 24 h. The false-positive rate was less than 1%, and an increased LD-1/total LD ratio had a predictive value of 96% for myocardial infarction. These results suggest that LD-1 is useful in the diagnosis of myocardial infarction on the first day of hospitalization.