Analytical aspects of the automated CKMB1,2 and CKMM1,2,3 isoform determination and its relation to other biochemical markers

Abstract

The automated (CK)MB1,2/MM1,2,3 isoform measurement, based on electrophoresis, has been simplified to the point that it has become possible to perform this analysis on a 24-h routine basis. We studied analytical aspects of this analysis and its clinical relevance in relation to other biochemical markers (CK total, CKMB activity, CKMB mass, myoglobin, Troponin I and Troponin T) in patients with acute myocardial infarction (AMI), patients with unstable angina pectoris (UAP), and healthy donors. Furthermore, the additional significance of the analysis was evaluated in patients with clinically unexpected, raised CKMB/CK total activities. The storage of serum at 4°C does not influence the MB2/MB1 ratios, whereas storage at 20°C changes them significantly. MM3/MM1 and normal MB2/MB1 ratios show lower coefficients of variation than increased MB2/MB1 ratios. Between 2 and 30 h after myocardial tissue damage, AMI patients showed a characteristic change in CK isoform patterns. At a mean time of 3.6 h after the onset of symptoms we found raised MB2/MB1 ratios in 94% of these patients. With the information of the CK isoform analysis unexpected abnormal CK activities could be explained by CK macro enzymes (Ig-bound and mitochondrial), insufficient CK clearance capacity, enzyme activities 4 h after (re-)infarction, and raised CK activity 15 h after skeletal muscle damage. We conclude that the CK isoforms are relatively simply to assess; they are adequate tools with which to indicate the CK kinetics over a period lasting between 2 and 30 h after tissue damage with a single blood sample and a single analysis; the CK isoform analysis has additional value in explaining inappropriate CKMB/CK total activities, and the MB2/MB1 ratios show to be one of the best early parameters for discriminating patients with AMI on admission to hospital.