MacroCreatineKinaseType 1 with ElectrophoreticMobilityIdenticalto That of the MB lsoenzyme

We describe the case of an elderly woman whose symptoms and electrocardiographic pattern initially suggested acute myocardial infarction. The value for total serum creatine kinase (EC 2.7.3.2; CK) was 737 U/L (reference interval: 22269 U/L), and electrophoresisfor CK isoenzymes demonstrated two bands, the more anodal migrating to the CK-MB region and the second migrating between the CK-MB and CK-MM regions. The above-normal total CK and electrophoretic pattern persisted dunng her 11-day hospital course. The QuiCK-MB (International Immunoassay Labs.) and TandemE CK-MB (Hybntech) immunoassays, however, showed CKMB mass measurements within the normal range. In further investigation with a mixture of patient’s serum and humanserum-based control containing all CK isoenzymes, the electrophoretic mobility of only CK-BB was altered, proving that the patient had antibody to the B unit of CK in her serum. Immunofixation revealed the more anodal band to be a CKIgA lambda complex, and the more cathodal band, a CK-lgG kappa complex. Mixing the patient’s serum with polyclonal antibody specific for CK-B slowed the electrophoretic mobility of only the more anodal band. Polyclonal antibody specificfor CK-M had no effect on either band. Evidently, this patient had two different types of macro CK type 1, both containing CKBB. We conclude that macro CK type 1 can mimic CK-MB and be a source of confusion.