Immunochemical CK-MB assay for myocardial infarction

The diagnostic efficiency of an immunochemical assay for CK-MB (I-MB) was compared with that of an electrophoretic procedure for this isoenzyme (E-MB) in 215 consecutive patients in whom acute myocardial infarction (MI) was clinically suspected. All patients were investigated with a standard protocol consisting of serial assays of total creatine kinase (CK) and lactic dehydrogenase (LD) activities, CK-MB and LD₁ isoenzymes, and electrocardiograms. Technetium pyrophosphate cardiac scans were obtained for eleven patients; autopsy was performed in six cases. The diagnosis of acute MI was established in 45 patients. The coefficients of variation for the intra-assay and interassay precision of I-MB assay ranged from 2.05%-7.2%. Concordance between the I-MB and E-MB results at the decision values for acute MI was observed in 203 of 215 patients (94.4%). At the cut-off point of 10 U/L, the I-MB assay was 95.5% sensitive and 95.3% specific for acute MI; the corresponding rates for the E-MB test were 93.3% and 94.7%, respectively. The test efficiency rate for I-MB assay was 95.3% and that of E-MB procedure 94.4%. A complete time-based isoenzyme protocol for the diagnosis of acute myocardial infarction has several variables; the need for interpretation of individual profiles and for the preparation of a formal report is discussed.