CPK; Creatine kinase; Creatine phosphokinase
A CPK is a blood test that measures creatine phosphokinase (CPK), an enzyme found predominantly in the heart, brain, and skeletal muscle. When the total CPK level is substantially elevated, it usually indicates injury or stress to one or more of these areas.
How the test is performed
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, 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 distend (fill with blood).
A needle is inserted into the vein, and the blood is collected in an airtight 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.
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.
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.
How to prepare for the test
Usually, no special preparation is necessary.
Infants and children:
The physical and psychological preparation a parent can provide for this or any test or procedure depends on the child’s age, interests, previous experiences, 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:
- Infant test or procedure preparation (birth to 1 year)
- Toddler test or procedure preparation (1 to 3 years)
- Preschooler test or procedure preparation (3 to 6 years)
- Schoolage test or procedure preparation (6 to 12 years)
- Adolescent test or procedure preparation (12 to 18 years)
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
When a muscle is damaged, CPK leaks into the bloodstream. Determining which isoenzyme (specific form of CPK) is elevated will help determine which tissue has been damaged.
This test may be used for the following reasons:
- Diagnose heart attack
- Evaluate cause of chest pain
- Determine the extent of muscle damage caused by drugs, trauma or immobility
- Detect early dermatomyositis and polymyositis
- Distinguish malignant hyperthermia from a postoperative infection
- Help discover carriers of muscular dystrophy (Duchenne)
Repeated checks of CPK levels may be performed. The pattern and timing of a rise and/or fall in CPK levels can be diagnostically significant, particularly if a heart attack is suspected.
What abnormal results mean
Higher than normal total CPK levels may be seen withconditions such as the following:
- hHeart attack
- Myocarditis (inflammation of the heart muscle)
- Central nervous system trauma or stroke
- Delirium tremens
- Dermatomyositis or polymyositis
- Electric shock
- Muscular dystrophies
- Pulmonary infarction (lung tissue death)
Additional conditions may give positive test results:
- Pericarditis following a heart attack
What the risks are
- 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 conducted to determine the exact location of muscle damage.
Factors that can affect test results include cardiac catheterization, intramuscular injections, trauma to muscles, recent surgery, and vigorous and prolonged exercise.
Drugs that can increase CPK measurements include amphotericin B, ampicillin, some anesthetics, anticoagulants, aspirin, clofibrate, dexamethasone, furosemide, morphine, 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.
by Janet G. Derge, M.D.
All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.