Cardiac enzyme studies measure the
levels of enzymes and proteins that are linked with injury of the heart muscle. These include the enzyme creatine kinase (CK), and
the proteins troponin I (TnI) and troponin T (TnT). Low levels
of these enzymes and proteins are normally found in your blood, but if your
heart muscle is injured, such as from a
heart attack, the enzymes and proteins leak out of
damaged heart muscle cells, and their levels in the bloodstream rise.
Because some of these enzymes and proteins are also found in other body
tissues, their levels in the blood may rise when those other tissues are
damaged. Cardiac enzyme studies must always be compared with your symptoms,
your physical examination findings, and
electrocardiogram (EKG, ECG) results.
Why It Is Done
Cardiac enzyme studies are done
Determine whether you are having a heart attack
or a threatened heart attack (unstable angina) if you have symptoms such as chest
pain, shortness of breath, nausea, sweating, and abnormal electrocardiography
Check for injury to the heart from other causes, such as an infection.
How To Prepare
No special preparation is required
before having this test.
Many medicines may affect the results of
this test. Be sure to tell your doctor about all the
nonprescription and prescription medicines you take.
Talk to your
doctor about any concerns you have regarding the need for the test, its risks,
how it will be done, or what the results will mean. To help you understand
the importance of this test, fill out the
medical test information form(What is a PDF document?).
How It Is Done
The health professional drawing your
Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.
Clean the needle site with
Put the needle into the vein. More than one needle stick
may be needed.
Attach a tube to the needle to fill it with
Remove the band from your arm when enough blood is
Put a gauze pad or cotton ball over the needle site as
the needle is removed.
Put pressure on the site and then put on a
Cardiac enzyme studies are often repeated over several
hours for comparison.
How It Feels
The blood sample is taken from a vein in
your arm. An elastic band is wrapped around your upper arm. It may feel tight.
You may feel nothing at all from the needle, or you may feel a quick sting or
There is very little chance of a problem from
having a blood sample taken from a vein.
You may get a small bruise at the site. You can
lower the chance of bruising by keeping pressure on the site for several
In rare cases, the vein may become swollen after the
blood sample is taken. This problem is called phlebitis. A warm compress can be
used several times a day to treat this.
Ongoing bleeding can be a
problem for people with bleeding disorders. Aspirin, warfarin (Coumadin) and
other blood-thinning medicines can make bleeding more likely. If you have
bleeding or clotting problems, or if you take blood-thinning medicine, tell
your doctor before your blood sample is taken.
Cardiac enzyme studies measure the
levels of the
enzyme creatine kinase (CK), and the proteins troponin I (TnI) and troponin T (TnT) in the blood.
and units for reporting the results of cardiac enzyme tests vary considerably. The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
CK-MB, which is found in large amounts in damaged heart
muscle is a more specific way to estimate the amount of heart muscle damage
than total CK. The total CK enzyme level can be elevated from vigorous
exercise, intramuscular injections, crush injuries to muscles, muscular
dystrophy, or muscle inflammation.
Fischbach FT, Dunning MB III, eds. (2009).
Manual of Laboratory and Diagnostic Tests, 8th ed.
Philadelphia: Lippincott Williams and Wilkins.
How this information was developed to help you make better health decisions.