CK-MB test

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.

CK-MB levels

Another way this works is by directly measuring how much CK-MB is in your blood. The reference range, the expected range for healthy adults, is different for men or people assigned male at birth (AMAB) and women or people assigned female at birth (AFAB).

• Women or people AFAB: Less than 4.4 ng/mL.
• Men or people AMAB: Less than 7.8 ng/mL.

*The unit of measurement for this is nanograms per milliliter or ng/mL. A small paper clip weighs about 1 gram, which is equal to 1 billion nanograms. There are 1,000 mL in a liter, which is equal to a little more than one-fourth of a gallon.

If your CK-MB level is higher than the reference range, it’s likely there’s damage to your heart muscle. However, a CK-MB test can’t tell the difference between heart muscle damage from a heart attack or other sources. That’s why other tests and diagnostic methods are so important for diagnosing a heart attack.

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.

Weaknesses of the CK-MB test

• Other CK-MB sources. Your skeletal muscles, which are the ones that help you move around, also have CK-MB in them in tiny amounts. In some instances, like very demanding physical exercise, those muscles can release CK-MB into your blood. Because this test can’t tell which muscles the CK-MB came from, the results might be confusing or unhelpful.
• Smaller window of testing. CK-MB doesn’t remain in your bloodstream as long as other chemical “markers” that show heart damage. CK-MB clears out of your body in about three days. On the other hand, troponin is detectable in your blood for up to three weeks.
• Interference from other conditions and procedures. Hypothyroidism, where your thyroid gland isn’t active enough, can make your CK-MB levels higher than normal. Those levels are also higher than normal if you’ve had heart surgery, inflammation in your heart, or had recent cardioversion (applying an electric shock to convert an abnormal heart rhythm back to a normal rhythm).

Strengths of the CK-MB test

Despite its weaknesses, the CK-MB test still has some advantages.

• Speed. CK-MB levels climb quickly after a heart attack, peaking about 12 hours after the attack. Troponin (either the I or T variants), the other test of choice, doesn’t peak until around 24 hours after a heart attack. (More sensitive troponin tests overcome this by improving the minimum amount of troponin they can detect, allowing for earlier detection.)
• Backup. Troponin testing might not always be available. When that’s the case, CK-MB is the next best lab test for heart attack.

When should I call my doctor?

CK-MB testing almost always happens while you’re a patient in a hospital emergency room or when you’re an inpatient. Because of that, it’s unlikely that you’ll need to call your doctor regarding this test. However, you can ask for sharing of records from your visit with your primary care provider and any other specialist providers you see. This is especially beneficial if you’re receiving care in a facility that doesn’t normally share information with your usual provider(s), such as when you’re traveling.

A note from Cleveland Clinic

A heart attack will likely be a scary medical event for you and your loved ones. Fortunately, there are testing methods that can help with a quick diagnosis, which means you can receive life-saving treatment fast. While CK-MB isn’t the test of choice like it was in years past, there are still times when it may be helpful.