Creatine kinase (CK or CPK) is an enzyme (a type of protein) found in muscle and brain. Normally, very little CK is found circulating in the blood. Elevated levels indicate damage to either muscle or brain; possibly from a myocardial infarction (heart attack), muscle disease, or stroke.

There are three types, or isoforms, of CK:

• CK-I, or BB, is produced primarily by brain and smooth muscle.
• CK-II, or MB, is produced primarily by heart muscle.
• CK-III, or MM, is produced primarily by skeletal muscle.

No special precautions are necessary, except in patients with a bleeding disorder.

A small amount of blood is drawn and used for laboratory analysis.

Physical activity may cause a rise in CK levels, especially the CK-III fraction. Therefore, patients should not engage in strenuous physical activity the day of the test. The patient should report any recent injections, falls, or bruises that have occurred, as these may elevate CK levels as well.

No aftercare is required, except to keep the puncture site clean while it heals.

There are no risks to this test beyond the very slight risk of infection at the puncture site.

In females, total CK should be 10–79 units per liter (U/L). In males, total CK should be 17–148 U/L. CK levels are reduced in the first half of pregnancy, and increased in the second half. CK levels are elevated in newborns.

The distribution of isoenzymes should be:

• CK-I: 0%
• CK-II: 0–5%
• CK-III: 95–100%.

Elevation of CK-I may be seen in stroke, extreme shock, or brain tumor.

Elevation of CK-II is seen after a myocardial infarction. It begins to rise three to six hours after the heart attack, and may peak within 24 hours. It should then return to normal. For this reason, it is a useful marker for recent myocardial infarction, but not for one which occurred more than a day before the test.

Elevation of CK-III indicates skeletal muscle damage. This may occur from normal exercise, trauma, or muscle disease. CK levels may be very high early on in muscular dystrophy, but may fall to normal later as muscle tissue is lost. Elevated CK is also seen in myositis, myoglobinuria, toxoplasmosis, and trichinosis. Hypothyroidism may also cause elevated CK.