[Macro-creatine kinase: not all increased CK-MB activity signifies a heart infarct]

Assay of creatine kinase MB isoenzyme plays an important role in the diagnosis of acute myocardial infarction. An increase in CK-MB is frequently interpreted by the clinician as objective evidence of myocardial cell damage. However, increases of CK-MB may be found in several circumstances in which patients have not sustained an acute myocardial infarction. An important cause of elevated CK-MB values unrelated to acute MI is the presence of macro-creatine kinases in the patient's plasma. With immuno-inhibition procedures macro-CK is often measured as CK-MB, leading to falsely elevated CK-MB. In this paper macro-CKs, their clinical importance and their interference with CK-MB determination are discussed.