Cardiac enzyme studies measure the levels of enzymes and proteins that are linked with injury of the heart muscle. The test checks for the proteins troponin I (TnI) and troponin T (TnT). The test might also check for an enzyme called creatine kinase (CK). Low levels of these proteins and enzymes are normally found in your blood, but if your heart muscle is injured, such as from a heart attack, the proteins and enzymes leak out of damaged heart muscle cells, and their levels in the bloodstream rise.
Because some of these proteins and enzymes 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 to:
- Determine whether you are having a heart attack or a threatened heart attack (acute coronary syndrome) if you have symptoms such as chest pain, shortness of breath, nausea, sweating, and abnormal electrocardiography results.
- 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 non-prescription 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 .
How It Is Done
The health professional drawing your blood will:
- 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 alcohol.
- Put the needle into the vein. More than one needle stick may be needed.
- Attach a tube to the needle to fill it with blood.
- Remove the band from your arm when enough blood is collected.
- 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 bandage.
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 pinch.
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 minutes.
- 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.
Cardiac enzyme studies measure the levels of the proteins troponin I (TnI) and troponin T (TnT) and the enzyme creatine kinase (CK) in the blood.
Values 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.
Troponin normal values:footnote 1
- TnI: Less than 0.12 micrograms per litre (mcg/L)
- TnT: Less than 0.01 mcg/L
CK-MB (creatine kinase-myocardial band) normal values:footnote 1
- 0–3 micrograms per litre (mcg/L)
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
- Other diseases, such as hypothyroidism, muscular dystrophy, certain autoimmune diseases, and Reye syndrome.
- Other heart conditions, such as myocarditis and some forms of cardiomyopathy.
- Emergency measures to treat heart problems, such as CPR, cardioversion, or defibrillation.
- Medicines, especially injections into muscles (IM injections).
- Cholesterol-lowering medicines (statins).
- Heavy alcohol use.
- Recent strenuous exercise.
- Kidney injury.
- Recent surgery or serious injury.
What To Think About
- 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 F, Dunning MB III (2015). Manual of Laboratory and Diagnostic Tests, 9th ed. Philadelphia: Wolters Kluwer Health.
Other Works Consulted
- Chernecky CC, Berger BJ (2013). Laboratory Tests and Diagnostic Procedures, 6th ed. St. Louis: Saunders.
- Pagana KD, Pagana TJ (2014). Mosby's Manual of Diagnostic and Laboratory Tests, 5th ed. St. Louis: Mosby.
- Thygesen K, et al. (2012). Third universal definition of myocardial infarction. Circulation, 126(16): 2020–2035. Also available online: http://circ.ahajournals.org/content/126/16/2020.
Current as of: August 31, 2020
Author: Healthwise Staff
Rakesh K. Pai MD, FACC - Cardiology, Electrophysiology
Brian D. O'Brien MD - Internal Medicine
E. Gregory Thompson MD - Internal Medicine
Adam Husney MD - Family Medicine
Martin J. Gabica MD - Family Medicine
George Philippides MD - Cardiology
Current as of: August 31, 2020