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CPK Blood Test: Diagnosing Muscle Damage

written by: Leigh A. Zaykoski•edited by: Leigh A. Zaykoski•updated: 5/4/2010

The CPK blood test is a laboratory test that measures creatine phosphokinase (CPK), which is one of the enzymes found in the brain, heart, and skeletal muscles. This is a useful test for helping doctors to diagnose problems such as muscle damage, heart attack, and related conditions.

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    Test Procedure

    Blood is drawn from a vein, usually from the arm. The venipuncture area is cleaned with alcohol or another antiseptic. A tourniquet is placed around the upper arm to cause the vein to swell with blood. The needle is inserted into the vein, and the blood is allowed to collect in a blood collection tube. During the blood draw, the tourniquet is removed to allow blood to circulate freely. Once the blood has been collected, the needle is removed from the puncture site, and pressure is placed on the site to help stop bleeding. For infants and children, a lancet is used to collect the blood sample. The blood is then placed on a slide or test strip. The puncture site is then covered with a bandage to help stop any bleeding.

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    When the CPK level in the blood is very high, it often means there has been injury or stress to the heart, skeletal muscle tissue, or even the brain. This is because CPK leaks into the bloodstream whenever this type of damage occurs. This test may be used to identify heart attack; determine the cause of chest pain; determine the level of muscle damage present; detect some conditions early; and give information about a patient's muscular dystrophy status. Hospitalized patients may have the CPK blood test performed on a daily basis for a period of several days. Gradual elevations in the level of CPK in the blood can help doctors diagnose serious conditions.

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    There are many conditions that can cause the results of a CPK blood test to be abnormal. These conditions include inflammation of the muscle of the heart; heart attack; stroke; inflammation of the skeletal muscles; muscular dystrophy; death of muscular tissue; and convulsions. Other conditions, such as hypothyroidism, can also cause abnormal test results.

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    If you have ever had a problem having blood drawn, let laboratory personnel know about the issue. They can take steps to ensure your comfort during the drawing of your blood sample.