Cardiac enzyme studies measure the levels of the enzyme creatine phosphokinase (CPK, CK) and the protein troponin (TnI, TnT) in the blood. 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 to:

• Determine whether you are having a heart attack or a threatened heart attack (unstable angina) if you have chest pain, shortness of breath, nausea, sweating, and abnormal electrocardiography results.
• Check for injury to the heart after bypass surgery.
• Determine if a procedure, such as percutaneous coronary intervention (PCI), or a medicine to dissolve the blockage (thrombolytic medicine) has successfully restored blood flow through a blocked coronary artery.

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 health professional 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 indicate. 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 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. Blood samples for these cardiac enzyme tests are usually drawn every 8 to 12 hours for 1 to 2 days after a suspected heart attack, to look for the rise and fall in the enzyme levels.

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.