creatine kinase-MB

Creatine kinase-MB is an enzyme found in relatively high amounts in heart muscle. For decades, before troponin assays existed, it was a leading blood marker for diagnosing a heart attack, because injured heart cells release it into the circulation.

Creatine kinase comes in several forms; the MB form is enriched in cardiac muscle but is also present in skeletal muscle. After a heart attack, CK-MB typically rises within a few hours, peaks around a day, and falls back over a couple of days. That predictable rise-and-fall once made it useful both for diagnosis and for estimating the size of an infarct.

Troponin has largely replaced CK-MB because troponin is more specific to the heart and stays elevated longer. CK-MB still has niche uses — for example, its faster return to normal can help detect a second, recurrent infarction — but in most modern settings it is a secondary or historical test rather than the first choice.