Creatine kinase MB isoforms for early diagnosis and monitoring of acute myocardial infarction

Abstract

MB isoforms of creatine kinase (ATP:creatine N-phosphotransferase, EC 2.7.3.2, CK) in 848 sera obtained from 80 patients with acute myocardial infarction (AMI) were studied by agarose gel isoelectric focusing. In 173 sera (20%) from 25 patients (31%), a new isoform designated as MB3 (p I 5.4) was detected at the cathodal side of MB2 (p I 5.2) in addition to the previously known MB2 and MB1 (p I 5.1). The new isoform MB3 was found in the extract of the cardiac muscle. MB3 was dominant in the sera at an earlier stage and a shorter period of time after AMI: 1–14 h (range), 1–29.5 h and 4–154 h for MB3, MB2 and MB1 dominant, respectively. MB3 was therefore found to be an earlier and a shorter phase indicator for AMI than MB2 or MB1. However, MB2 > 1 was the most prevalent pattern at the time of admission to the hospital. In AMI, specificity was 96.2%, 92.4% and 90.6%, and sensitivity was 20.4%, 88.9% and 97.6%, for MB3, MB2 and MB1 isoforms, respectively. CK-MB isoform patterns were biased to MB1 dominant in the deceased group, and to MB2 dominant in the surviving group. Therefore determination of CK-MB isoforms is also useful in the course of observation of AMI. The fourth isoform, MB0 (p I 5.0), was detected at the anodal side of MB1. MB0 was a minor band of the CK-MB isoform which appeared when serum CK-MB activity increased.