CPK isoenzymes

How the Test is Performed:
Adult or child:
Blood is drawn from a vein ( venipuncture ), usually from the inside of the elbow or the back of the hand. 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 restrict blood flow through the vein. This causes veins below the tourniquet to distend (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. Once the blood has been collected, 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. 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. The pattern of a rise or fall in CPK or CPK isoenzymes can be diagnostically significant.

How to Prepare:
Adults:
Usually no special preparation is necessary.

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:



How it Feels:
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing .

Risks:

  • excessive bleeding
  • fainting or feeling lightheaded
  • hematoma (blood accumulating under the skin)
  • infection (a slight risk any time the skin is broken)
  • multiple punctures to locate veins



Why this Test is Performed:
CPK isoenzymes are performed when the total CPK level is elevated, to help differentiate the damaged source tissue.

CPK is an enzyme found predominantly in the heart, brain, and skeletal muscle . CPK is found in 3 forms (isoenzymes), which differ slightly in structure. CPK-1 (also called CPK-BB) is in highest amounts in the brain, CPK-2 (also called CPK-MB) is high in the heart, and CPK-3 (also called CPK-MM) is high in skeletal muscle.

CPK-MB levels rise 3 to 6 hours after a myocardial infarction ( heart attack ) occurs. 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 , 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, cerebrovascular accident , and pulmonary infarction) are associated with elevated levels of this isoenzyme.

The CPK-MM isoenzyme normally comprises almost all the serum CPK enzyme activity in healthy people. When the total CPK level is substantially elevated, it usually indicates injury or stress to the skeletal muscle.

This test is used to:



Normal Values:
CPK-MM: 0 to 100%
CPK-MB: 0 to 5%
CPK-BB: 0%

Abnormal Results:
Higher-than-normal CPK-1 levels may indicate:

Higher-than-normal CPK-2 levels may indicate:

Just after a heart attack (2 to 3 hours), there is a significant rise in CPK-2 levels. The level increases with the severity of the heart attack. CPK levels remain elevated up to 24-hours after a heart attack.

Higher-than-normal CPK-3 levels may indicate:

Additional conditions under which the test may be performed:



Cost:
The estimated cost is $61.

Special Considerations:
Factors that can affect test results include cardiac catheterization , intramuscular injections, recent surgery, and vigorous and prolonged exercise .

Drugs that can increase CPK measurements include amphotericin B, ampicillin, some anesthetics, anticoagulants, aspirin, clofibrate, dexamethasone, furosemide and morphine.

The total CPK test is about 70% accurate because there are many causes of elevated levels. Isoenzyme testing for individual types of CPK is about 90% accurate.

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 from some people may be more difficult than from others.