CK-MB Fractionation

This test measures total creatine kinase (CK) and CK-MB, one of the CK isoenzymes, and may be useful in assessing patients with suspected acute coronary syndrome or reinfarction when troponin T and I testing are not available [1].

CK is a dimeric enzyme that exists in 3 isoenzymes: CK-BB, CK-MM and CK-MB. CK-MM is the primary isoenzyme found in the skeletal muscle and heart tissue. CK-BB is mainly found in the brain and smooth muscle of gastrointestinal track and urinary bladder. CK-MB is mainly found in the heart with a small amount in skeletal muscle [2].

The quantitation of CK-MB levels in serum was widely used to diagnose acute myocardial infarction before troponin T and I levels were adopted for better cardiac-specificity [1,3]. When troponin T and I testing are not available, CK-MB measurement, preferably expressed as CK-MB relative to the total CK level, may help evaluate myocardial injury if skeletal muscle damage is excluded [1,2]. Routine CK-MB testing or CK-MB testing in addition to cardiac troponin for chest pain is not recommended [1, 3].

In individuals with chronic muscle damage/disease or chronic renal failure, CK-MB may account for the elevation of CK levels owing to the phenomenon of "fetal reversion" [2].

The results of this test should be interpreted in the context of pertinent clinical and family history and physical examination findings.

References
1. CKMB: optimal testing recommendations. AACC. Accessed October 11, 2022. https://www.aacc.org/advocacy-and-outreach/optimal-testing-guide-to-lab-test-utilization/a-f/ckmb
2. Panteghini M, et al. Serum enzymes. In: Rifai N, et al. eds. Tietz Textbook of Laboratory Medicine. 7th ed. Elservier Inc; 2022:4149-4299.
3. Gulati M, et al. Circulation. 2021;144(22):e368- e454.