A case of abnormally high CK-MB protein concentration caused by IgM-human anti-mouse antibody

Abstract

We encountered a patient with a false high concentration of creatine kinase-MB (CK-MB) protein. In this patient, despite a low total CK activity of 14 U/L, the CK-MB protein concentration was as high as 177.2 ng/mL. However, the troponin T concentration was lower than the cut-off value. Also, there were no abnormalities in the CK isozyme pattern and reaction time course in this patient as determined by the CK-MB mass assay. Furthermore, no dilution linearity was confirmed. In this patient, the IgM concentration was high and the CK-MB protein concentration did not decrease after the heat inactivation test. In the dithiothreitol treatment and human anti-mouse antibody (HAMA) absorption test, the measured values in this patient’s serum were significantly reduced. In conclusion, the abnormally high CK-MB protein concentration in this patient was revealed to be due to a nonspecific reaction caused by IgM-HAMA.