Ratio of CK-MB to total CK, cardiac index
This test measures the amount of creatine kinase (CK), an enzyme, in your blood.
Your body makes many forms of CK, including CK-MB. CK is found in the heart, muscles, and other organs including the small intestine and uterus. If you have a heart attack, injured heart muscle cells release CK into your blood.
Because many tissues contain CK, high levels of CK can be a sign of a variety of problems. Higher CK-MB may point more specifically to heart damage.
Each year millions of Americans visit the emergency room with chest pain, but only a fraction of those people are actually having a heart attack or another serious, sudden heart problem. This test helps your doctor figure out whether you're having a heart attack.
Measuring the ratio of CK-MB to total CK can provide information about the cause of your symptoms.
You may have this test if your doctor suspects you are having a heart attack. Symptoms of a heart attack often include:
Pain or discomfort in the chest, such as a squeezing sensation or feeling of fullness
Pain in the neck, back, arm, or jaw
Shortness of breath
Lightheadedness or dizziness
Nausea or vomiting
Your doctor may also order a test to measure cardiac troponin, or CTn. This test is more commonly used than CK-MB because it more specifically shows heart damage.
Your doctor may also order an electrocardiogram, or ECG, to measure electrical activity in your heart and help diagnose a heart attack.
Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.
Levels of CK-MB may not rise in your blood within the first six hours after a heart attack. You may need to have repeated tests to see if you've had a heart attack.
If you've had a heart attack, both CK-MB and the ratio of CK-MB to total CK will rise. The higher the ratio of CK-MB to CK, the more likely it is that you have a heart problem.
Higher levels of CK-MB may also be caused by muscle damage elsewhere in your body, by diseases that affect your muscles, and by trauma to your chest.
This test may not be helpful if you have both heart and other muscle damage at the same time.
The test requires a blood sample, which is drawn through a needle from a vein in your arm.
Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.
Timing is important. If you have the test too soon after a heart attack, your results may not be accurate.
Strenuous exercise and cocaine use can also affect your results.
You don't need to prepare for this test. But be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.