56 Creatine kinase MB (CK-MB)

Creatine kinase MB: cardiac isoenzyme, time course after myocardial infarction and comparison with troponin.

Creatine kinase MB (CK-MB) is the isoenzyme of creatine kinase found mainly in heart muscle, where it makes up a much larger share of CK activity than in skeletal muscle. When heart muscle cells die, as in myocardial infarction, CK-MB is released into the blood. For decades it was the main laboratory marker of heart attack. Today cardiac troponin is the preferred biomarker because it is more sensitive and more specific. CK-MB is used when troponin is not available.

HeartMyocardial infarctionBiomarkers

Rises after infarction≈ 3–6 h

Peak≈ 12–24 h

Returns to normal≈ 2–3 days

Preferred markercardiac troponin

Figure 1. Schematic time course of CK-MB and troponin after myocardial infarction. Troponin may remain raised for up to about two weeks; the exact timing depends on infarct size, reperfusion and the assay.

Clinical use

CK-MB is interpreted together with total CK: a CK-MB share of more than a few percent of total CK points to heart muscle as the source. Because CK-MB returns to normal within 2–3 days, it was historically used to detect a new infarction soon after a first one. The current universal definition of myocardial infarction relies on a rise and/or fall of cardiac troponin; when troponin is not available, CK-MB measured by mass assay is the best alternative.

Other causes of raised CK-MB

Myocarditis, cardiac surgery, cardioversion, coronary intervention, cardiac contusion
Severe skeletal muscle damage (rhabdomyolysis, muscular dystrophy, polymyositis) and in marathon runners, as regenerating skeletal muscle contains more CK-MB
Kidney failure, hypothyroidism, some tumours; macro-CK can give falsely high results

Seek emergency care

Call emergency services immediately for chest pain or pressure lasting more than a few minutes, especially with breathlessness, sweating, nausea or pain spreading to the arm, neck or jaw. Do not wait for blood test results.

References

Thygesen K, Alpert JS, Jaffe AS, et al. Fourth universal definition of myocardial infarction (2018). Eur Heart J. 2019;40(3):237–269. doi:10.1093/eurheartj/ehy462

This article is for general information and does not replace a consultation with a doctor. Laboratory results must be interpreted by a physician together with symptoms and other tests.

Published on 29 April 2024