Evaluation of three current methods for the determination of creatine kinase-MB catalytic activity

Three current methods for the determination of the creatine kinase-MB activity were evaluated: electrophoresis (Beckman Inst.), ion-exchange MB-Zyme (J.T. Baker) and ion-exchange on aca (Du Pont). Eighty patients were selected out of three groups: acute myocardial infarction, heart and vascular surgery patients and a number of noncardiac cases. The precision of the ion-exchange methods was comparable; CV 5.7% (aca) and CV 5.2% (MB-Zyme) for a high creatine kinase-MB pool. Electrophoresis overestimated the creatine/kinase-MB/activity and was less precise (CV 9.6%) and less sensitive than the ion-exchange methods. The aca (Du Pont) method was less specific than the MB-Zyme. The main source of discrepancy was samples from certain patients in the surgery unit, which gave falsely high value by the aca method, and showed altered mobility in electrophoresis, suggesting an atypical creatine kinase. Three macro creatine kinase type I included in this study were erroneously determined as creatine kinase-MB by both the ion-exchange methods.