An increase in the creatinine kinase MB iso-enzyme (CKMB) can be caused by?

Appeared in: RAK Nursing Officer - 2019

Explanation

Creatine Kinase-MB (CK-MB) is an isoenzyme found predominantly in the heart muscle.
Damage or death (necrosis) of myocardial cells causes them to release CK-MB into the bloodstream.
Elevated serum CK-MB is a specific and well-established biomarker for diagnosing acute myocardial infarction (heart attack).
The level of CK-MB typically begins to rise 4-6 hours after the onset of chest pain, peaks at 12-24 hours, and returns to normal within 48-72 hours.

Option A: Cerebral bleeding involves damage to brain tissue, which would lead to an increase in the CK-BB isoenzyme, not CK-MB.
Option B: An intramuscular injection causes trauma to skeletal muscle, which primarily releases the CK-MM isoenzyme. The effect on CK-MB is negligible.
Option C: Damage to skeletal muscle from a fall primarily releases the CK-MM isoenzyme. While severe skeletal muscle injury can cause a minor elevation in CK-MB, it is not the specific or primary indicator; myocardial necrosis is.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Cardiac Biomarkers and Myocardial Infarction as background academic context rather than a clinical decision trigger.
Nurses play a critical role in collecting blood samples for serial cardiac marker tests (e.g., at presentation, and then 3-6 hours later) for patients with suspected MI.
Understanding the different isoenzymes prevents misinterpretation. A high total CK with normal CK-MB and high CK-MM points towards skeletal muscle injury, not a heart attack, guiding appropriate care.
Prompt identification of elevated CK-MB allows for rapid initiation of treatments like thrombolysis or percutaneous coronary intervention (PCI) to restore blood flow and save heart muscle.

How to Approach the Question

First, identify the key term in the question: 'creatinine kinase MB iso-enzyme (CKMB)'.
Recall the three main isoenzymes of creatine kinase (CK-MM, CK-MB, CK-BB) and their primary tissue locations.
Associate CK-MB specifically with heart muscle.
Evaluate the options based on this association. Which option involves damage to the heart muscle?
Cerebral bleeding involves the brain (CK-BB). IM injection and falls involve skeletal muscle (CK-MM). Myocardial necrosis is death of heart muscle tissue.
Conclude that myocardial necrosis is the only condition listed that would cause a significant and specific increase in CK-MB.

Concept Tested & Keywords

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E6 PATHOLOGY QUICK REVIEWBased on Harsh Mohan Textbook of PATHOLOGY pp. 196-198, 13-15

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