Creatine Phosphokinase (CPK)

Definition
Purpose
Precautions
Description of CPK Isoenzyme Testing
Preparation
Aftercare
Risks
Normal Results

Definition

Creatine phosphokinase or CPK is an enzyme found in cells that is used to turn creatine into phosphate. This phosphate is a quick source of cellular energy. Muscle cells are the primary source of CPK in the body. The CPK test measures the amount of CPK present in the bloodstream.

Purpose

Because damaged muscle tissue releases CPK into the blood, the detected levels are an indication of the extent and time of the damage. There are different forms of CPK (CPK isoenzymes) that can help determine what tissue has been damaged.

Precautions

There are many variables that contribute to the amount of enzymes present in the bloodstream, including a person’s activity level and even if a person is taking a certain type of medication or drug. In a healthy adult, the normal range of total CPK falls between 22 to 198 (units per liter). CPK levels higher than this indicate that muscle damage has occurred. If the CPK test result is elevated, further tests are performed to determine where the muscle damage occurred. There are many causes for elevated levels of CPK. For this reason, the general total CPK test is only approximately 70% accurate. The CPK isoenzyme testing is more specific and therefore approximately 90% accurate.

Drugs that may increase CPK levels:

• Ampicillen
• Anticoagulants
• Alcohol
• Cocaine
• Aspirin
• Morphine
• Furosemide
• Dexamethasone
• Clofibrate
• Amphotericin B
• Isotretinoin (acne treatment)
• Some anesthetics

Description of CPK Isoenzyme Testing

CPK is composed of three different isoenzymes:

• CPK-1 (CPK-BB) is concentrated in the brain and lungs
• CPK-2 (CPK-MB)is found mostly in heart tissue
• CPK-3 (CPK-MM)is found mostly in skeletal muscle

If the level of CPK-1 is elevated that would indicate that the damage occurred to the brain or lung tissue. For the brain, this could mean, a stroke, brain cancer, brain injury, or a seizure. For the lungs, elevated levels could indicate a pulmonary embolism. If the level of CPK-2 is elevated, that would indicate that the damage has occurred in the heart tissue. For the heart, this could mean a heart attack has occurred.

KEY TERMS

Myocarditis— Inflammation of the muscles of the walls of the heart due to a viral infection.

Myositis— Inflammation of muscle tissue.

Pulmonary embolism— A blood clot in the lungs.

CPK-2 levels rise 3-6 hours after a heart attack, peak at 12-24 hours and will return to normal 12-48 hours after tissue damage occurs. Elevated CPK-2 levels could also indicate other heart trauma, myocarditis, or electrical injuries. CPK-3 levels that are elevated usually indicate an injury or stress to skeletal muscle. For skeletal muscle this could indicate strenuous exercise, seizures, injury or trauma to muscle tissue, multiple intramuscular injections, myositis or muscular dystrophy. Individuals who are affected with certain types of muscular dystrophy may have levels of CPK as high as 15,000 to 35,000 (units per liter).

Preparation

CPK levels are obtained by a routine blood draw. There is no preparation for the blood draw, except that individuals should avoid vigorous or prolonged exercise prior to the test. The test may be repeated several times over a period of time to look for significant rising or falling of the CPK levels.

Aftercare

Aftercare following a routine blood test consists of care of the area around the puncture site. Pressure is applied for a few seconds prior to covering the wound with a bandage.

Risks

The risks associated with routine blood draw include bruising, swelling or excessive bleeding from the puncture site and dizziness or fainting may occur during or shortly after the blood draw.

Normal Results

As stated above, in a healthy adult, the normal range of total CPK falls between 22 to 198 (units per liter).

Resources

BOOKS

Segen, J.C. and J. Wade. Patient’s Guide to Medical Tests: Everything You Need to Know About the Tests Your Doctor Orders. New York, Checkmark Books, 2002.

PERIODICALS

Kymak, Y. “Creatine Phosphokinase Values During Iso-tretinoin Treatment For Acne.” International Journal of Dermatology 47 (April 2008): 398–401.

OTHER

GeneTests, 9725 Third Avenue NE, Suite 602, Seattle, WA 98115. Funded by the National Institutes of Health. http://www.genetests.org.

Medline Plus, A service of the U.S. National Library of Medicine and the NIH, 8600 Rockville Pike, Bethesda, MD 20894. http://www.nlm.nih.gov/medlineplus/ency/article/003503.htm.

Renee Laux, M.S.

Creatinine test seeKidney function tests