- creatine kinase-isoenzymes
- creatine phosphokinase-isoenzymes
This test measures the blood levels of three forms of the enzyme creatine phosphokinase, which is also called CPK. These forms are known as isoenzymes.
How is the test performed?
In order to measure the amount of CPK isoenzymes in the blood, a blood sample is taken from a vein on the forearm or hand. First, the skin over the vein is cleaned with an antiseptic. Next, a rubber tube called a tourniquet is tied around the upper arm. This enlarges the veins in the lower arm by restricting blood flow through them. A fine needle is gently inserted into a vein, and the tourniquet is removed. Blood flows from the vein through the needle and is collected in a syringe or vial for testing in the laboratory. After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.
What is involved in preparation for the test?
Normally, no preparation is required for this test.
What do the test results mean?
If a disease process is taking place, the total amount of CPK will be high, and the individual isoenzyme increases are used to determine what part of the body is responsible for the increase in total CPK. For example, when a heart attack occurs, the total CPK becomes high because of an increase in the CPK-MB and CPK-MM isoenzymes. The normal total CPK level is roughly 25 to 175 units per liter.
With a heart attack, normal values for each of the isoenzymes are as follows:
- CPK-BB: 0% of the total CPK
- CPK-MB: 0% to 6% of the total CPK
- CPK-MM: 96% to 100% of the total CPK
Abnormally high levels of CPK-BB may sometimes be seen in the following:
- lung damage from a blood clot (pulmonary embolus)
- after cardiopulmonary resuscitation (CPR)
Abnormally high levels of CPK-MB may indicate the following:
- heart attack
- any other trauma to the heart, such as from heart surgery
- electrical injuries
Abnormally high levels of CPK-MM may indicate the following:
- heart attack
- muscle damage
- intramuscular injections
- muscular dystrophy
- myositis, an inflammation in the muscles usually due to infection or immune system disease
- recent surgery
- rhabdomyolysis, which is widespread muscle destruction, usually due to alcoholism or exercise
- strenuous exercise
- as a side effect of taking certain drugs, such as statins