Determination of creatine kinase MB activity with the Du Pont aca: interferences from the sample matrix

During the last three years we and other have observed discrepancies between results for creatine kinase isoenzyme MB as measured with the mechanized ion-exchange chromatographic method in the Du Pont aca and those by other techniques. These observations prompted us to investigate the influence of the matrix on the Du Pont CK-MB assay. We conclude that, apart from possible interferences by CK-MM, CK-BB, and both types of macro CK, the aca will give apparent CK-MB activities that are directly related to protein concentration and inversely related to sodium chloride concentration. Practical consequences for the routine and emergency laboratories are: no diluted samples are allowed; application is restricted to samples from patients suspected of acute myocardial infarction which show upper-normal total CK activity; and multiple timed samples are run, in order to recognize the typical change in enzyme pattern with time.