CPK isoenzymes test

Definition

The CPK isoenzymes test measures the different forms of creatine phosphokinase (CPK) in the blood. CPK is an enzyme found mainly in the heart, brain, and skeletal muscle.

See also: Creatine phosphokinase test

Alternative Names

Creatine phosphokinase - isoenzymes; Creatine kinase - isoenzymes; CK - isoenzymes

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.

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.

How to prepare for the test

Usually, no special preparation is necessary.

Tell your doctor about all the medications you are taking. Certain medications can interfere with test results. Drugs that can increase CPK measurements include the following:

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

This test is done if a CPK test reveals that your total CPK level is elevated. CPK isoenzyme testing can help pinpoint the exact soure of the damaged tissue.

CPK is made of three slightly different substances:

• CPK-1 (also called CPK-BB) is found mostly 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

What abnormal results mean

Higher-than-normal CPK-1 levels:

Because CPK-1 is found mostly in the brain and lungs, injury to either of these areas can increase CPK-1 levels. Increased CPK-1 levels may be due to:

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

Higher-than-normal CPK-2 levels:

CPK-2 levels rise 3 - 6 hours after a heart attack. If there is no further heart muscle damage, the level peaks at 12 - 24 hours and returns to normal 12 - 48 hours after tissue death.

Increased CPK-2 levels may also be due to:

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

CPK-2 levels do NOT usually rise with chest pain caused by angina, pulmonary embolism (blood clot in the lung), or congestive heart failure.

Higher-than-normal CPK-3 levels are usually a sign of muscle injury or muscle stress and may be due to:

• Crush injuries
• Muscle damage due to drugs or being immobile for a long time (rhabdomyolysis)
• Muscular dystrophy
• Myositis (skeletal muscle inflammation)
• Receiving many intramuscular injections
• Recent nerve and muscle function testing (electromyography)
• Recent seizures
• Recent surgery
• Strenuous exercise

Special considerations

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

Isoenzyme testing for specific conditions is about 90% accurate.

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.