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.