The CPK isoenzymes test measures the different forms of creatine phosphokinase in the blood.

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.

If you are in the hospital, this test may be repeated over 2 or 3 days. A significant rise or fall in the total CPK or CPK isoenzymes can help your health care provider diagnosis certain conditions.

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.

CPK isoenzymes are performed when the total CPK level is elevated. Isoenzyme testing can help differentiate the source of the damaged tissue.

CPK is an enzyme found predominantly in the heart, brain, and skeletal muscle. CPK is composed of 3 isoenzymes that differ slightly in structure:

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

Because the CPK-1 isoenzyme is predominately found in the brain and lungs, injury to either of these organs (for example, stroke or lung injury due to a pulmonary embolism) are associated with elevated levels of this isoenzyme.

CPK-2 levels rise 3 - 6 hours after a heart attack. If there is no further damage to the heart muscle, the level peaks at 12 - 24 hours and returns to normal 12 - 48 hours after tissue death. CPK-2 levels do not usually rise with chest pain caused by angina, pulmonary embolism (blood clot in the lung), or congestive heart failure.

The CPK-3 isoenzyme is normally responsible for almost all CPK enzyme activity in healthy people. When this particular isoenzyme is elevated, it usually indicates injury or stress to skeletal muscle.

Higher-than-normal CPK-1 levels may occur with the following:

• Brain cancer
• Brain injury (due to trauma, stroke, or bleeding in the brain)
• Electroconvulsive therapy
• Pulmonary infarction
• Seizure

• Heart attack
  • There is a significant rise in CPK-2 levels in the first 2 - 3 hours after a heart attack. This test is used to diagnose a heart attack.

  • The extent of the elevation depends on the severity of the heart attack. CPK levels may remain elevated up to 24 hours after a heart attack, and sometimes even longer.

• Myocarditis (inflammation of the heart muscle usually due to a virus)
• Electrical injuries
• Trauma to the heart (for instance, from a car accident)
• Heart defibrillation (purposeful shocking of the heart by medical personnel)
• Open heart surgery

Higher-than-normal CPK-3 levels may occur with the following:

• Crush injuries of skeletal muscle
• Multiple intramuscular injections
• Muscular dystrophy
• Myositis (skeletal muscle inflammation)
• Post-electromyography (a test of nerve and muscle function)
• Recent seizures
• Recent surgery
• Rhabdomyolysis (skeletal muscle damage due to drugs or prolonged immobilization)
• Strenuous exercise

Factors that can affect test results include cardiac catheterization, intramuscular injections, recent surgery, and vigorous and prolonged exercise or immobilization.

Drugs that can increase CPK measurements include the following:

• Amphotericin B
• Ampicillin
• Some anesthetics
• Anticoagulants
• Aspirin
• Clofibrate
• Dexamethasone
• Furosemide
• Morphine
• Alcohol
• Cocaine

Isoenzyme testing for specific conditions is about 90% accurate.