This is one of the most sensitive indicators of myocardial injury. Creatine kinase is found primarily in the heart, skeletal muscle, and brain. Acute liver damage has no effect on CK. CK may be elevated in acute muscular damage (such as seen with hypodermic injections), hepatic coma, and delirium tremens.
The specimen should be drawn before injection or at least one hour after injection. Trauma to muscle during surgery makes CK unreliable for a few postoperative days.
Isoenzyme determinations of CK are also becoming widely available today. There are three major categories: CK-BB (as found in brain and lung), CK-MM (as found in skeletal muscle), and the hybrid CK-MB (in cardiac muscle).
The CK-MB level begins to rise 3-6 hours after onset of infarct, peaks in 12-24 hours, and returns to normal in 24-48 hours. There is a rough correlation between the size of the infarct and the degree of CK-MB isoenzyme elevation.
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