Is a CPK Isoenzymes Test?
Enzymes are complex proteins that facilitate chemical changes in
every part of the body. Your body needs enzymes in order to work properly. An
enzyme called creatine phosphokinase (CPK) is important for muscle function. The
CPK isoenzymes test is a way to measure the levels of this enzyme in your bloodstream.
CPK can be broken down into three separate parts:
- CPK-1 is mainly found in your brain and lungs.
- CPK-2 is mostly found in your heart.
- CPK-3 is found in your skeletal muscle.
When these parts of your body become damaged due to injury or
disease, CPK enzymes can be released into your bloodstream. The CPK isoenzymes
test checks the levels of these enzymes in your blood. This can help your doctor
identify the areas of your body that have been damaged.
The CPK isoenzymes test is a simple blood test that involves
minimal preparation and risk. The blood sample will be sent to a laboratory for
analysis, and your doctor will explain the results to you.
The CPK isoenzymes test may still be used in some cases, but over
the past decade, most doctors have transitioned away from this test. Instead, a
troponin test is often performed to evaluate damage to your heart muscle. A troponin
test measures the levels of proteins called troponin T and troponin I in the
blood. These proteins are released when your heart muscle becomes damaged due
to a heart attack or other serious heart condition. The troponin test procedure
is similar to that of a CPK isoenzymes test.
Is a CPK Isoenzymes Test Done?
A CPK isoenzymes test is usually done in the emergency room if
you have the symptoms of a heart attack. Your doctor may order a CPK blood test
- help them diagnose a heart attack
- find the cause of your chest pain
- find out how much heart or muscle tissue has
The test can also determine whether you carry the gene for
muscular dystrophy. Muscular dystrophy is a group of diseases that causes
muscle loss and weakness over time. A CPK isoenzymes test can detect various
muscle diseases, including:
which is an inflammatory disease that affects the skin and muscles
- polymyositis, which is an inflammatory disease
that causes muscle weakness
- malignant hyperthermia, which is an inherited
disease that causes muscle contractions
Do I Prepare for a CPK Test?
The CPK isoenzymes test is similar to other blood tests. It
doesn’t require any fasting or special preparation.
Before you schedule your blood test, it’s important to tell your
doctor about any over-the-counter and prescription medications you’re taking.
Some substances can interfere with the test results, including:
- drugs that lower cholesterol
- amphotericin B, which is an antifungal medication
Other factors may also interfere with test results, including:
- vigorous exercise
- recent surgery
- intramuscular injections, such as vaccines
- cardiac catheterization, which is when a
catheter is inserted into a vein in your arm, groin, or neck and threaded to
Make sure to tell your doctor if you’ve recently experienced any
of these events.
Can I Expect During a CPK Test?
The blood test should only take a few minutes.
A 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. They’ll tie an elastic band around your upper arm to create pressure
and make it easier to find your vein.
Once they find your vein, they’ll insert a sterile needle into the
vein and draw your blood into a small vial. You may feel a slight prick as the
needle goes in, but the test itself isn’t painful. After the vial is filled,
the needle and elastic band will be removed. A bandage will then be placed over
the puncture site.
The vial will be labeled and sent to a laboratory. Results will
be sent 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. Varying levels can help with
Your arm may feel sore where the needle was inserted. You might also
have some mild bruising or throbbing near the puncture site temporarily. You’ll
likely feel more discomfort if the healthcare provider had difficulty accessing
a vein and multiple puncture wounds were made.
Most people don’t have any serious or lasting side effects. Rare
complications of a blood test include:
- excessive bleeding
- infection, which is a risk whenever your skin is
Call your doctor immediately if you experience any of these
CPK-1 is found primarily in your brain and lungs. Elevated CPK-1
levels could indicate:
- a brain injury due to stroke or bleeding in the
- a seizure
- brain cancer
- a pulmonary infarction, or the death of lung
CPK-2 is found mostly in your heart. Elevated levels of CPK-2 can
be the result of:
- injury to your heart due to an accident
- inflammation of your heart muscle, which is
usually from a virus
- an electrical injury
Increased levels of CPK-2 in the blood can also occur after open heart
surgery and heart defibrillation, which is a medical procedure that involves
shocking your heart. After a heart attack, CPK-2 levels in your blood rise, but
they usually fall again within 48 hours.
CPK-3 is found in your skeletal muscle. The levels of CPK-3 may
rise if your muscles:
- are damaged from a crush injury, which occurs when
a body part has been squeezed between two heavy objects
- have been immobile for an extended period
- are damaged by illegal drug use
- are inflamed
Other factors that contribute to high levels of CPK-3 include:
- muscular dystrophy
- muscle trauma, which can occur from participating
in contact sports, being burned, or having surgery
- electromyography, which is a procedure that tests
nerve and muscle function
It’s important to remember that results will vary from person-to-person,
depending on specific injuries and conditions. Your doctor will explain what
your results mean and describe your treatment options.