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The Cardiac Enzyme Test...

What it is, what it reveals, and how it is part of a heart attack treatment

The cardiac enzyme test allows your doctor to use the predictable pattern of enzyme release after a heart attack to diagnose your condition.

If you've been to emergency with a suspected heart attack, or if you are known to have had a heart attack, you will very likely have had these tests.

But... you may not have known they were measuring your enzymes since it is analysis of your blood sample in a lab that reveals your enzyme levels.

The reason for the test is simple: your blood enzymes change in response to a heart attack. It's one of the best markers for revealing whether or not a myocardial infarction (heart attack) has taken place and to assess the degree of heart muscle damage.

An important tool

Cardiac enzyme tests have become an important tool in the diagnosis and treatment of heart attacks.

Damage to the heart muscle as the result of a heart attack causes certain enzymes and proteins to leak into the bloodstream.

When the levels of these enzymes and proteins are viewed in conjunction with with other tests such as electrocardiograms, the results reveal whether a heart attack took place as well as its severity.

Frequency of tests

Generally your blood will be taken about every eight hours over a period of one or two days after a heart event.

Your doctors will be watching for changes in the enzyme levels.

Predictable patterns are known to take place, so your enzyme results can be compared to these known levels.

Be sure to tell your doctor or nurse about any medications you are taking because these can alter the test results.

What enzymes are measured?

Creatine kinase (CK), the protein troponin (Tnl), and the protein myoglobin are the three that are most commonly measured.

The test for CK can measure total creatine kinase levels; however, The American College of Cardiology recommends breaking out CK-MB (CK2), the CK enzyme found in the heart.

Myoglobin is more rapidly released than the other two, so readings of this protein are useful for an early diagnosis.

CK-MB and Tnl rise within six to eight hours after a heart attack, with the highest reading coming within 24 hours.

Tnl falls back to normal within 10 days, while CK returns to normal within three to four days. Because of this, tests can be conducted several days after a suspected heart attack and still provide useful information.

When cardiac enzyme tests are not useful

There are times when this test may not be helpful. These include:

  • someone on cholesterol lowering medications (statins)
  • heavy alcohol use
  • recent heavy exercise
  • a recent serious injury
  • recent surgery
  • having had CPR or defibrillation
  • kidney failure

What the tests reveal

Cardiac enzyme tests tell your health care team whether you have suffered a heart attack, the severity of the attack, the possible onset of a heart attack, and they help them to monitor your treatment.

For your part, you need do nothing except provide some blood! After that it's up to your doctor to use the results to help in your diagnosis and treatment.


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