Creatine phosphokinase test

Definition

Creatine phosphokinase (CPK) is an enzyme found mainly in the heart, brain, and skeletal muscle. This article discusses the test to measure the amount of CPK in the blood.

See also: CPK isoenzymes

Alternative Names

CPK test; Creatine kinase

How the test is performed

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

The blood sample is sent to a lab, where the amount of CPK is measured.

This test may be repeated over 2 or 3 days for if you are a patient in the hospital.

How to prepare for the test

Usually, no special preparation is necessary.

Tell your doctor about any medications you are taking. Drugs that can increase CPK measurements include amphotericin B, ampicillin, certain anesthetics, blood thinners, aspirin, clofibrate, dexamethasone, furosemide, alcohol, and cocaine.

How the test will feel

When the needle is inserted to draw blood, you may feel moderate pain, or only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed

When the total CPK level is very high, it usually means there has been injury or stress to the heart, the brain, or muscle tissue. For example, when a muscle is damaged, CPK leaks into the bloodstream. Determining which specific form of CPK is high helps doctor's determine which tissue has been damaged.

This test may be used to:

• Diagnose heart attack
• Evaluate cause of chest pain
• Determine if or how badly a muscle is damaged
• Detect early dermatomyositis and polymyositis
• Tell the difference between malignant hyperthermia and postoperative infection
• Reveal who carries muscular dystrophy (Duchenne)

The pattern and timing of a rise or fall in CPK levels can be diagnostically significant, particularly if a heart attack is suspected.

Normal Values

What abnormal results mean

High CPK levels may be seen in patients who have:

• Heart attack
• Brain injury or stroke
• Inflammation of the heart muscle (myocarditis)
• Convulsions
• Delirium tremens
• Dermatomyositis or polymyositis
• Electric shock
• Lung tissue death (pulmonary infarction)
• Muscular dystrophies

Additional conditions may give positive test results:

• Hypothyroidism
• Hyperthyroidism
• Pericarditis following a heart attack
• Rhabdomyolysis

What the risks are

There is very little risk involved with having your blood taken. Veins and arteries vary in size from one patient to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Special considerations

Other tests should be done to determine the exact location of muscle damage.

Factors that may affect test results include cardiac catheterization, intramuscular injections, trauma to muscles, recent surgery, and heavy exercise.

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References

Anderson JL. ST segment elevation acute myocardial infarction and complications of myocardial infarction. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 72.

Barohn RJ. Muscle diseases. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 447.