Macro-creatine kinase as an interference in CK isoenzyme determinations.

Creatine kinase (CK) isoenzyme determinations have been performed on a series of specimens containing macro-CK, an atypical isoenzyme variant seen in approximately 1% of patients. These specimens were obtained from 2 different patients. Isoenzyme determinations were made using four different methods: electrophoresis (Corning ACI), column chromatography (Dupont ACA), immunoinhibition (ESKACHEM), Smith Kline), and immunoprecipitation (Isomune-CK, Roche). In specimens containing macro-CK, electrophoresis showed no false-positive CK-MB determinations, and immunoprecipitation showed 1 in 8 false-positives, while column chromatography and immunoinhibition each showed 4 of 4 false positives. When utilizing these methods, the possibility of false-positive CK-MB determinations must be taken into consideration as a possible explanation for positive CK-MB results which do not agree with the clinical assessment of the patient.