What Is a CPK Isoenzymes Test?
Enzymes are complex proteins that facilitate chemical changes in every part of the body. Your body needs enzymes to function. The CPK isoenzymes test is a way to measure the levels of an enzyme called creatine phosphokinase (CPK) in your blood.
CPK can be broken down into three distinct parts:
- CPK-1 comes mainly from the brain and lungs
- CPK-2 is mainly from the heart
- CPK-3 is from skeletal muscle.
When these parts of your body suffer damage due to injury or disease, CPK isoenzymes can be released into your bloodstream. Checking the levels of these enzymes in your bloodstream can help doctors identify the areas of your body that have been damaged.
The CPK isoenzymes test is a simple blood test requiring almost no preparation and involves minimal risk. The blood sample will be sent to a laboratory for analysis and your doctor will explain the results to you.
Purpose of CPK Test
A CPK blood test is generally ordered when people go to an emergency room with symptoms of a heart attack. Your doctor may order a CPK blood test to:
- help diagnose a heart attack
- investigate chest pain
- find out how much heart or muscle tissue has been damaged
The test can also determine whether you carry the gene for muscular dystrophy. It can detect dermatomyositis (a muscle disease), polymyositis (an inflammatory disease that affects muscle tissue), and malignant hyperthermia, an inherited disease that is exacerbated by general anesthesia.
Preparation for the Blood Test
The CPK isoenzymes blood test is performed just like other routine blood tests. The actual blood analysis takes place in a laboratory. No fasting or special preparation on the part of the patient is required.
Before scheduling your blood test, it is important to tell your doctor about any over-the-counter and prescription medications you take. Some substances that can interfere with the test results are:
- drugs that lower cholesterol
- amphotericin B (an antifungal medication)
Other factors may also interfere with test results, including:
- vigorous exercise
- prolonged immobility
- intramuscular injections
- cardiac catheterization
- recent surgery
Be sure to discuss these events with your doctor prior to taking the blood test.
How the Blood Test Works
The blood test should take only a few minutes.
Your healthcare provider will use a topical antiseptic to clean a small area of your arm, usually on the inside of your elbow or on the back of your hand. An elastic band will then be wrapped around your upper arm to create pressure and make it easier to access a vein.
A needle will be inserted into your vein and blood drawn into a small vial. You will probably feel the stick of the needle or a stinging sensation. After the vial is filled, the elastic band and the needle will be removed. A bandage will be placed over the puncture site.
The vial will be labeled and sent to a laboratory. Results will be forwarded to your doctor, who will explain them to you.
In some cases, your doctor may want to repeat the test over several days to see if your enzyme levels change. Changing levels can help with the diagnosis.
Your arm may feel sore where the needle was inserted and you might have some mild bruising or throbbing for a short while. You will likely have more discomfort in rare instances when the healthcare provider has difficulty accessing a vein.
Most people have no serious or lasting side effects. Rare complications of a blood test include:
- infection (a risk whenever skin is pierced)
If you experience any of these symptoms, contact your doctor immediately.
Analyzing the Results
CPK-1 is found primarily in the brain and lungs. Elevated CPK-1 levels could indicate:
- brain injury, stroke, or bleeding
- brain cancer
- pulmonary infarction (death to an area of the lung)
CPK-2 is found in the heart. Elevated levels of CPK-2 can be the result of:
- injury to the heart (due to accident)
- inflammation of the heart muscle (usually from a virus)
- electrical injuries
The presence of high levels of CPK-2 in the blood can also follow heart defibrillation and open heart surgery. After a heart attack, CPK-2 levels in the blood rise, but usually fall again within 48 hours.
Congestive heart failure, angina, or pulmonary embolisms generally do not cause CPK-2 to rise in the bloodstream.
Levels of CPK-3 may rise in the bloodstream if muscles:
- are damaged from a crush injury (when a body part has been squeezed between two heavy objects)
- have been immobile for a long period
- are damaged by drugs
- are inflamed
Other factors that contribute to high levels of CPK-3 include:
- muscular dystrophy
- muscle trauma (from contact sports, burns, and surgery)
- electromyography (testing of nerves and muscle function)
Results will vary from person to person, depending on specific injuries and conditions. Your doctor will explain what your specific results mean, and discuss the most effective form of treatment.