Abstract
Serial measurements of the MB isoenzyme of creatine kinase, total creatine kinase, aspartate mainotransferase, and urea stable lactate dehydrogenase have been made in the serum of a series of 139 patients admitted with a diagnosis of suspected myocardial infarction. Serum MB isoenzyme measurements have also been made on postoperative surgical patients and patients with medical disorders known to have caused raised serum total creatine kinase activity. All these enzymes were abnormal in at least one specimen from all patients with electrocardiographically proved acute myocardial infarction. The magnitude of the MB isoenzyme rise was 2 to 3 times greater than that of any of the other enzymes. The duration of its rise was relatively short. The MB isoenzyme was more specific for myocardial infarction than other enzymes and no increases were found in postoperative patients, except in those after cardiac bypass surgery. The MB isoenzyme seems the most sensitive and specific test for myocardial infarction available, though there are technical problems in its accurate measurement.