IgA-CK-BB complex with CK-MB electrophoretic mobility can lead to erroneous diagnosis of acute myocardial infarction.

This patient, on admission, presented with a tentative diagnosis of myocardial infarction: the electrocardiogram showed a nonspecific ST-segment and T-wave abnormalities, and total creatine kinase (CK; EC 2.7.3.2) activity was slightly increased (238 U/L). However, a high electrophoretic value for CK-MB (50% of total CK activity) and the electrophoretic pattern of lactate dehydrogenase (EC 1.1.1.27) isoenzymes ruled out myocardial infarction. The isoenzyme migrating as CK-MB was found later to contain no immunologically normal CK-M subunits, and it was bound to IgA. A mixture of the patient's serum and a human serum control containing all CK isoenzymes showed altered electrophoretic mobility only for CK-BB, indicating that the patient's serum contained antibodies to the B unit of CK. Elution from a Sephadex G-200 column showed that the peak at which most of the anodic CK was eluted corresponded to a molecular mass of approximately 200 kDa. Evidently this atypical isoenzyme was an IgA-CK-BB complex. Because this macro CK type 1 can mimic CK-MB, it may therefore be a source of confusion.

Abnormal electrophoretic mobility of creatine kinase isoenzyme in serum of an otherwise healthy person.

We describe the abnormal electrophoretic mobility of a creatine kinase isoenzyme in the serum of an apparently healthy individual. In agarose gel electrophoresis this isoenzyme migrates more toward the cathode than does the MM isoenzyme. It is more resistant to heat and more strongly inhibited by urea than the normal MM isoenzyme. We performed gel filtration, on a Sephadex G-200 column, of the patient's serum and observed two distinct isoenzymes with different relative molecular masses; a normal isoenzyme of 80,000 daltons and another abnormal one of 240,000 daltons. We performed serum immunoelectrophoresis but did not observe any immune complex formation involving the abnormal isoenzyme.