RESUMO
To evaluate a method to quantitate the isoforms of serum creatine kinase isoenzyme MM (CK-MM) by agarose gel electrophoresis, sera of normal subjects (n = 74) and patients with acute myocardial infarction (n = 21) and other diseases (n = 67) were studied. The within-assay imprecision (CV) for CK-MM1, -MM2, and -MM3 was 1.9%, 0.8%, and 2.2% at the activity of 79, 105, and 64 U/L (30 degrees C, CK-NAC), respectively; while the assay-to-assay imprecision was 4.8%, 3.2% and 3.9%, respectively. The method could detect 5 U/L or more of any CK-MM isoform and was linear with respect to CK activity at values less than 1100 U/L. Sera from healthy subjects (n = 74) contained mainly CK-MM1 (mean = 48.5%), with lesser amounts of CK-MM2 (mean = 30.6%) and CK-MM3 (mean = 20.8%). The central 95-percentile reference range for the ratio of MM3/MM1 was 0.12-1.34 with mean = 0.49. The sensitivity of CK-MM3/MM1 ratio greater than 1.3 in the diagnosis of acute myocardial infarction employing the first available sample was 90% at a specificity of 91%, compared with a sensitivity of 81% and specificity of 87% for the conventional CK-MB assay. At CK-MM3/MM1 ratio of 1.6 or more, the specificity increased to 96% while sensitivity remained unchanged at 90%. This procedure for the quantitation of serum CK-MM isoforms is convenient, practical and suitable for inclusion in the routine panel of cardiac tests.
