CK-MB assays used in cardiac damage diagnosis are immunoassay measurements rather than enzyme assays that measure the activity of CK-MB itself. Although CK-MB is predominantly located in heart muscle, it is not 100% specific for myocardium. Trace amounts of CK-MB are also present in skeletal muscle; therefore, skeletal muscle injury can cause CK-MB elevations. Some laboratories measure total CK and if elevated, reflex to CK-MB testing.
Normal CK-MB values for adults are typically < 5.0 ng/mL.
