Two weeks after a myocardial infarction, which laboratory value shows muscle damage?

• A. Creatine Kinase
• B. Troponin I
• C. Myoglobin
• D. ALT

Answer: (A)

When muscle tissue is damaged, enzymes stored inside muscle cells leak into the bloodstream. Creatine kinase is one of those enzymes and is present in both skeletal and cardiac muscle, so its elevation signals muscle injury in general. In the setting of a myocardial infarction, damage to heart muscle can lead to a rise in CK (including the CK-MB isoenzyme), reflecting the muscle injury that occurred.

Troponin I is highly specific for cardiac muscle injury and stays elevated for a longer window, but it’s a more specific cardiac marker rather than a general indicator of muscle damage. Myoglobin appears very early after injury but is not specific to cardiac muscle and falls back to normal quickly. ALT is a liver enzyme and does not reflect muscle damage.

So the marker that best represents muscle damage among these options is creatine kinase.