A CPK is a blood test that measures creatine phosphokinase (CPK), an enzyme found mainly in the heart, brain, and skeletal muscle.

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. 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, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any bleeding.

This test may be repeated over 2 or 3 days for a hospitalized patient. The pattern of a rise or fall in CPK (or CPK isoenzymes) can be diagnostically significant.

Usually, no special preparation is necessary.

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.

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 exact tissue has been damaged.

This test may be used to:

• Diagnose heart attack
• Evaluate cause of chest pain
• Determine 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.

High CPK levels may be seen in patients who have:

• Heart attack
• Myocarditis (inflammation of the heart muscle)
• Central nervous system trauma or stroke
• Convulsions
• Delirium tremens
• Dermatomyositis or polymyositis
• Electric shock
• Muscular dystrophies
• Pulmonary infarction (lung tissue death)

• Hypothyroidism
• Pericarditis following a heart attack
• Rhabdomyolysis

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

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.

Drugs that can increase CPK measurements include amphotericin B, ampicillin, some anesthetics, blood thinners, aspirin, clofibrate, dexamethasone, furosemide, alcohol, and cocaine.

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample may be more difficult from some people than from others.