What is the CK-MB test?

The CK-MB test is a test that looks for a specific type of enzyme in your blood to diagnose or rule out a heart attack. However, CK-MB is no longer the blood test of choice for diagnosing heart attacks, and many hospitals no longer use it because there are better test methods available (the cardiac troponin tests are currently the tests of choice).


What is CK-MB?

Creatine kinase (CK) is an enzyme (a molecule that helps speed up certain chemical reactions) that occurs naturally inside muscle cells throughout your body. Different forms of CK occur in different places, and most of the myocardial band (MB) version of this enzyme occurs in muscle cells in your heart.

How does this test work?

Damage to heart muscle cells causes CK-MB — as well as several other proteins and enzymes — to leak into your blood. This test can detect how much CK-MB enzyme is in your blood. If there’s more CK-MB in your blood than there should be, it can be a sign you’ve had a heart attack.

CK-MB is also a time-sensitive test. The level of CK-MB in your blood will rise sharply after a heart attack and then return to normal after two or three days.

Why is this test performed?

CK-MB can be found in heart muscle, making it useful for detecting any kind of injury to your heart. However, other muscles also contain CK-MB, which is why tests for cardiac troponin (which is specific to your heart) are now the tests of choice.

When and where is this test performed?

Because it’s useful for diagnosing heart attacks, which are life-threatening medical emergencies, a hospital emergency room is where most CK-MB tests happen. However, you might also undergo a CK-MB test when you’re a patient in a hospital if your healthcare provider suspects a heart attack or other injury to your heart.

Who performs this procedure?

CK-MB testing involves several medical professionals. This usually (but not always) includes the following:

  • A healthcare provider — usually a doctor — who orders the test.
  • A phlebotomist (a nurse, technician or nursing assistant with special training and experience in drawing blood), who collects the blood sample.
  • Lab staff, who run the test and send the results back to the provider who ordered the test.

Can I prepare for it, and what should I expect?

Because heart attacks aren’t predictable, it usually isn’t possible to prepare for this test.

Important: If you take Vitamin B7, also known as biotin, tell your provider about this as soon as possible before they take a blood sample. Biotin can interfere with the test results, which is important information for your provider to have as they care for you. Depending on what dose of biotin you take and when you last took it, you may need to wait to give a blood sample for this test (this doesn’t apply to tests in urgent or emergency situations).

What can I expect during the test?

The test starts with a phlebotomist who will draw blood from a vein, usually one in your arm or hand. If you already have an intravenous line inserted into a vein, they may be able to get the sample from that line.

What can I expect after the test?

Depending on the testing technology available, some labs can run this test in less than 20 minutes. The provider who ordered the test will review the results and discuss them with you.

It’s common for providers to order repeats of this test (this is called serial testing) to track your CK-MB levels over time. Having a timeline of results can sometimes help rule out a heart attack. However, repeating the test may change when your provider discusses your results with you.

What are the risks of this test? Are there side effects?

The most common side effects of this test, if the sample came directly from a vein and not from an IV line, are mild bruising or soreness.


What type of results will I get, and what do the results mean?

Depending on the type of CK-MB test, the results can take on different forms.

Percentage of CK-MB in total CK

One method involves testing total CK levels and determining what percentage of that amount was CK-MB. A normal result for this test is under 4%. This is because small amounts of CK-MB from muscle tissue other than your heart often enter your blood. When the total CK-MB makes up more than 4% of the total CK, it’s very likely that there’s damage to your heart muscle.

What are the advantages and disadvantages of the CK-MB test?

For years, the CK-MB test had a key role in helping diagnose heart attacks. However, the CK-MB test has a few weaknesses that put it behind other tests.