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Blood test
Blood test

CPK isoenzymes
Definition:
A blood test that measures the isoenzymes (different forms) of creatine phosphokinase.
Alternative Names:
Creatine phosphokinase - isoenzymes; Creatine kinase - isoenzymes; CK - isoenzymes
How the test is performed:
Adult or child:
Blood is drawn from a vein (venipuncture), usually in the arm. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band or blood pressure cuff) is placed around the upper arm to apply pressure and cause veins below the tourniquet to fill 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 tourniquet is removed to restore circulation and facilitate the collection of blood. Once the proper amount of blood has been drawn, the needle is removed, and the puncture site is covered to stop any bleeding.

Infant or young child:
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 piece of cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

This test may be repeated over 2 or 3 days for hospitalized people. A significant rise or fall in the total CPK or CPK isoenzymes can be very helpful to healthcare providers for the diagnosis of certain conditions.
How to prepare for the test:
Adults:
Usually no special preparation is necessary.

Infants and children:
The physical and psychological preparation involved in readying a child for any test or procedure depends on the child's age, interests, previous experiences, and level of trust. For specific information on how to prepare your child based on their age, see the following topics:

How the test will feel:
When the needle is inserted to draw blood, some people may feel moderate pain, while others may feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed:
CPK isoenzymes are performed when the total CPK level is elevated and 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 forms (isoenzymes), which differ slightly in structure. CPK-1 (also called CPK-BB) is concentrated in the brain, CPK-2 (also called CPK-MB) is found mostly in the heart, and CPK-3 (also called CPK-MM) is found mostly in skeletal muscle.

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

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

The CPK-MM isoenzyme normally comprises almost all the total CPK enzyme activity in healthy people. When this particular isoenzyme is elevated, it usually indicates injury or stress to the skeletal muscle.
What abnormal results mean:
Higher-than-normal CPK-1 (BB) levels may occur with: Higher-than-normal CPK-2 (MB) levels may occur with:
  • heart attack
  • myocarditis (inflammation of the heart muscle mostly due to viruses)
  • 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
Just after a heart attack (2 to 3 hours), there is a significant rise in CPK-2 (MB) levels; this is why doctors rely on this test for the diagnosis of 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.

Higher-than-normal CPK-3 (MM) levels may occur with:

Special considerations:
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 amphotericin B, ampicillin, some anesthetics, anticoagulants, aspirin, clofibrate, dexamethasone, furosemide and morphine, alcohol, and cocaine.

Isoenzyme testing for specific conditions is about 90% accurate.
Review Date: 12/5/2001
Reviewed By: Steven Angelo, M.D. Department of Internal Medicine, Yale School of Medicine, Hospital of Saint Raphael, New Haven, CT. Review provided by VeriMed Healthcare Network.

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