How is creatine kinase-MB (CK-MB) used as a cardiac marker?

Updated: Jul 30, 2021
  • Author: Kamal (Komo) Gursahani, MD, MBA; Chief Editor: Barry E Brenner, MD, PhD, FACEP  more...
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Answer

Prior to the introduction of cardiac troponins, the biochemical marker of choice for the diagnosis of acute MI was the CK-MB isoenzyme. The criterion most commonly used for the diagnosis of acute MI was two serial CK-MB elevations above the diagnostic cutoff level or a single result more than twice the upper limit of normal. Although CK-MB is more concentrated in the myocardium, it also exists in skeletal muscle and false-positive elevations occur in a number of clinical settings, including trauma, heavy exertion, and myopathy.

CK-MB first appears 4-6 hours after symptom onset, peaks at 24 hours, and returns to normal in 48-72 hours. Its value in the early and late (>72 h) diagnosis of acute MI is limited. However, its release kinetics can assist in diagnosing reinfarction if levels rise after initially declining following acute MI.

In the Can Rapid Risk Stratification of Unstable Angina Patients Suppress Adverse Outcomes with Early Implementation of the ACC/AHA Guidelines (CRUSADE) registry, a review of almost 30,000 patients revealed that discordant troponin and CK-MB results occurred in 28% of patients. [45] However, patients who were troponin negative but CK-MB positive had in-hospital mortality rates that were not significantly increased from patients who were negative for both biomarkers.

Similarly, in a report of more than 10,000 patients with ACS from the multicenter Global Registry of Acute Coronary Events (GRACE) registry, in-hospital mortality was highest when both troponin and CK-MB were positive, intermediate in troponin-positive/CK-MB-negative patients, and lowest in patients in whom both markers were negative and in those who were troponin negative/CK-MB positive. [46] Thus, an isolated CK-MB elevation has limited prognostic value in patients with a non-ST elevation ACS.

Despite updates to guidelines promoting cardiac troponin as the only cardiac biomarker necessary to diagnose MI, biomarker protocols vary across the United States. A 2017 survey of 824 US hospitals undergoing Chest Pain Center accreditation by the Society of Cardiovascular Patient Care revealed that only 24% use cardiac troponin alone, 49% use the 99th percentile of the upper reference limit for their cut point, and most use both cardiac troponins and CK-MB in serial measurements to rule out MI. [47]


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