Lab Test: Creatine Kinase MB Level
- Suspected acute coronary syndrome - elevated biomarkers should be obtained from at least 2 successive blood samples in order to diagnose myocardial infarction (MI).
- An elevated CK-MB is defined as a value that exceeds the 99th percentile of CK-MB values in a reference control group.When evaluating suspected ongoing or reinfarction and the initial troponin level is high, sequential samples of a more rapidly appearing biomarker such as CK-MB or myoglobin may be employed to clarify the timing of the MI. Increased CK-MB usually appears at about 6 hours and peaks at 24 hours post-infarction. Persistent elevation beyond 96 hours may suggest ongoing myocardial necrosis. The reappearance of elevated CK-MB levels suggests extension of infarction.
- Diagnosing suspected recurrent MI after ST-segment elevation MI (STEMI) using CK-MB:
- If initial CK-MB elevation was greater than upper limit of normal (ULN):
- Within 18 hours of STEMI: use recurrent ST-segment elevation on ECG and at least one supportive finding: chest pain or hemodynamic compromise
- More than 18 hours after STEMI: increase in CK-MB by at least 50%
- If initial CK-MB was less than ULN: increase in CK-MB
- Within 24 hours of percutaneous coronary intervention (PCI), use either:
- CK-MB more than 3 times ULN
- New Q waves
- Within 24 hours of CABG, use either:
- CK-MB more than 10 times UL
- CK-MB t times ULN and new Q waves
- False-positive elevations are more commonly seen with total CK levels rather than CK-MB levels. CK-MB should be obtained upon presentation in all patients with possible acute coronary syndrome and repeated 6 to 12 hours after symptom onset if required for diagnosis.
- Suspected myocardial contusion - with significant contusion, CK-MB elevation may be present on admission and may clear within 24 hours. Elevated values have been used as a means of diagnosis; however, their value as a screening test is highly questionable. A CK-MB ratio greater than 5% is consistent with myocardial injury. A blow to the chest may be strong enough to produce cardiac arrhythmias without actual myocardial cell necrosis (cardiac concussion or commotion cardis). Such patients will have ECG abnormalities with normal CK-MB values
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