Cardiac Enzyme Studies

Cardiac Enzyme Studies

Test Overview

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

  • Determine whether you are having a heart attack
    or acute coronary syndrome 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
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
  • 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.


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.

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

CK-MB (creatine kinase-myocardial band) normal values:footnote 1

  • 0–3 micrograms per liter (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
  • Emergency measures to
    treat heart problems, such as
    CPR, cardioversion, or
  • Medicines, especially injections into muscles (IM
  • Cholesterol-lowering medicines
  • Heavy alcohol use.
  • Recent strenuous
  • 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.



  1. Fischbach F, Dunning MB III (2015). A 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.
  • Fischbach F, Dunning MB III (2015). A Manual of Laboratory and Diagnostic Tests, 9th ed. Philadelphia: Wolters Kluwer Health.
  • 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:


ByHealthwise StaffPrimary Medical Reviewer Rakesh K. Pai, MD, FACC - Cardiology, Electrophysiology E. Gregory Thompson, MD - Internal Medicine Martin J. Gabica, MD - Family Medicine Adam Husney, MD - Family Medicine Specialist Medical Reviewer George Philippides, MD - Cardiology

Current as ofFebruary 23, 2018

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