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

Updated: Nov 20, 2018
  • Author: Donald Schreiber, MD, CM; 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 2 serial 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 CRUSADE registry, a review of almost 30,000 patients revealed that discordant troponin and CK-MB results occurred in 28% of patients. 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. [33]

Similarly, in a report of more than 10,000 patients with ACS from the multicenter 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. [34] Thus, an isolated CK-MB elevation has limited prognostic value in patients with a non-ST elevation ACS


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