CK-MD remains useful alongside troponin testing in which scenario, and what is a major limitation of CK-MB measurement?

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CK-MB is especially useful alongside troponin testing for detecting reinfarction. After an initial myocardial infarction, troponin stays elevated for days, but a second heart injury will cause CK-MB to rise again and then fall, providing a clear signal of a new infarct when the troponin pattern alone would be confusing. This kinetic pattern—a new CK-MB rise after the troponin has already peaked or begun to fall—is why CK-MB remains helpful in this scenario.

A major limitation of CK-MB measurement is that it is not perfectly specific to myocardial tissue. CK-MB can be elevated in skeletal muscle injury, surgery, or other conditions that raise CK isoenzymes, and older assays could show cross-reactivity with CK-MM. Because troponin is more specific to cardiac injury, CK-MB’s role is mainly in identifying reinfarction through its rise-and-fall pattern rather than diagnosing the initial MI.