Cardiac Enzymes

Cardiac enzymes are proteins in the heart muscle cells. They have different roles in the heart muscle. Doctors use various laboratory tests to check enzyme levels. These tests help determine if chest pain or other symptoms are heart-related.Other names for a cardiac enzyme test include cardiac marker or biomarker test and myocardial serum marker test.

This article explains cardiac enzymes, including why doctors measure them and what the results mean.

Cardiac enzymes refer to protein components Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source inside heart muscle cells. Measuring them in the blood is an important tool doctors have for diagnosing the cause of chest pain. Their presence in the blood indicates that the heart may have sustained damage.

The three main cardiac enzymes that doctors can test for are:

This article goes into detail about what these three cardiac enzyme tests may reveal.

Doctors do not routinely check these cardiac enzymes:

Another cardiac enzyme, heart-type fatty acid binding protein, is not used in the United States. In some settings, it has shown higher sensitivity to heart damage. However, it is not as specific as troponin. More research is necessary to properly define its role in diagnosing a heart attack.

A cardiac enzyme test measures the amount of heart biomarkers in the blood. Today, the main Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source test is troponin, but doctors may also order CK and myoglobin on occasion. High levels of cardiac enzymes may indicate a heart attack or other heart conditions.

The main use of a cardiac enzyme test is to help diagnose or rule out a heart attack. Doctors may also order cardiac enzyme tests to monitor the heart after cardiac surgery or procedures, such as angioplasty.

Recent research suggests that cardiac enzyme tests may be useful after noncardiac surgery in some cases. Mainly, it may help identify potential heart injury after surgery in people at high risk of cardiovascular disease.

Doctors are most likely to order a cardiac enzyme test if you have symptoms of a heart attack.

Symptoms of a potential heart attack Trusted Source American Heart Association Highly respected national organization Go to source include:

Seek immediate medical care (call 911) for any of these serious symptoms.

Currently Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source, doctors are most likely to order a troponin test to evaluate the heart. They may also order a CK test or a myoglobin test in some cases.

Lab test reference ranges can vary from one lab to another. Your doctor will share cardiac enzyme test results with you and let you know what they reveal.

There are a few different troponin assays available, and they are not equivalent. This makes it tricky to interpret them and define normal levels. There is also a standard troponin test and a high-sensitivity version.

Normally, troponin is not detectable in the blood of healthy people. A high troponin level is anything above the 99th percentile of the upper reference limit for any particular test. This means the level is higher than 99% of what you would see in a healthy control population.

A standard troponin test measures two troponin components, cardiac troponin I (cTnI) and cardiac troponin T (cTnT). They are measured in nanograms per milliliter (ng/ml). A general reference range for standard troponin tests includes:

For a high-sensitivity cTnT test, the general cutoff at the upper reference limit is given in nanograms per liter (ng/l) and is sex specific:

There are different forms of the CK cardiac enzyme. The one most useful Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source to doctors trying to diagnose a heart attack is creatine kinase-MB (CK-MB).

Generally, a normal range for CK is 20–200 international units per liter (IU/l). Anything above this would be high. However, this range may vary by race and sex in healthy people.

CK-MB should be less than 5% of the total CK test value.

A general cutoff for a myoglobin blood test is less than 100 micrograms per liter (mcg/l) or ng/ml.

The meaning of high cardiac enzyme levels depends on which enzyme and what other conditions you have. Your doctor will look at your entire clinical picture when interpreting test results.

The main cause of a high troponin level is a heart attack. However, there are several other cardiac- and noncardiac-related conditions that can increase troponin.

CK-MB can be high after a heart attack. However, it can also be high Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source when there is skeletal muscle damage or after extreme exercise.

Likewise, myoglobin levels can be high after both a heart attack and acute skeletal muscle injury.

Cardiac enzyme tests are blood tests Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source. This usually involves drawing blood from a vein in your arm. Most people will have a catheter placed in an arm vein after admission to the emergency room. If you do not have one, collecting the sample will involve inserting a small needle.

The results typically come back within 60 minutes. Repeat tests are often necessary while diagnosing a heart attack.

Here are some questions people often ask about cardiac enzymes.

There can be several Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source causes of elevated cardiac enzymes. A heart attack is the major one that doctors try to rule out or confirm using cardiac enzymes. Troponin is the most utilized test for identifying a heart attack. However, other causes can increase troponin and other cardiac enzyme levels.

Your doctor will advise you about the next steps in the diagnostic process Trusted Source PubMed Central Highly respected database from the National Institutes of Health Go to source if cardiac enzyme levels are high. This may involve more testing or procedures, such as angioplasty.

Cardiac enzyme tests are a diagnostic tool doctors use to evaluate chest pain and other symptoms of a heart attack. Troponin is the main test because it is most specific to heart muscle damage. Other conditions can raise troponin and other cardiac enzyme tests. Still, cardiac enzyme tests allow doctors to quickly evaluate the possibility of heart muscle damage.