Analysis of a blood sample can provide important information about the heart. Some of the more significant blood components that may be measured include the following:
Apolipoproteins—the protein component of lipoproteins—are not included in a standard lipid profile, but may be tested separately. Abnormal levels may promote atherosclerosis, and may increase the risk of coronary artery disease (CAD) and stroke.
Homocysteine is an amino acid (protein building block). Elevated blood levels may promote atherosclerosis and CAD, as well as blood clots that can lead to a heart attack or stroke.
C-reactive protein (CRP) is a substance that reflects low levels of systemic inflammation and is increased in people at risk for CAD.
Cardiac enzyme studies measure certain enzymes, such as CK-MB, that are released in large amounts when the heart is diseased or damaged, as from a heart attack.
Purpose of the Cardiac Blood Tests
- Apolipoproteins, homocysteine, and CRP are measured to evaluate the risk of CAD.
- Cardiac enzymes help to detect the presence of a recent or ongoing heart attack; to determine the timing of a heart attack and assess the degree of damage to the heart muscle; to determine the appropriateness of thrombolytic therapy (a treatment that is beneficial only during an ongoing heart attack); and to monitor any shortage of blood to the heart after cardiac surgery or catheterization.
Who Performs Cardiac Blood Tests
- A doctor, a nurse, or a lab technician
Special Concerns about Cardiac Blood Tests
- Pregnancy, oral contraceptives, cortisone medications, and nonsteroidal anti-inflammatory drugs (such as ibuprofen) may affect CRP in your blood and interfere with results.
- Intramuscular injections, strenuous exercise, recent surgery, and a variety of medications can raise levels of cardiac enzymes and interfere with results.
Before the Cardiac Blood Tests
- A 12- to 14-hour fast is required before measuring apolipoproteins (water is permitted).
- Report to your doctor any medications, herbs, or supplements you are taking. You may be advised to discontinue certain of these agents before the test. In particular, alcohol, aminocaproic acid (Amicar), and lithium should be withheld before testing for cardiac enzymes, if possible.
- No special preparations are needed before testing homocysteine or CRP.
What You Experience
- A sample of your blood is drawn from a vein, usually in your arm, and sent to a laboratory for analysis.
- Subsequent blood samples may be needed to measure cardiac enzymes after a heart attack (for example, 6, 12, and 24 hours after the episode and daily thereafter).
Risks and Complications of Cardiac Blood Tests
After the Cardiac Blood Tests
- After blood is drawn, pressure is applied (with cotton or gauze) to the puncture site.
- Resume your normal diet and any medications withheld before the test.
- Blood may collect and clot under the skin (hematoma) at the puncture site; this is harmless and will resolve on its own. For a large hematoma that causes swelling and discomfort, apply ice initially; after 24 hours, use warm, moist compresses to help dissolve the clotted blood.
Cardiac Blood Test Results
- Abnormal apolipoprotein levels—such as an increased level of lipoprotein(a), or Lp(a)—may significantly increase your risk for CAD and heart attack. Lifestyle measures, such as diet and exercise, and lipid-lowering medications may decrease this risk.
- A high homocysteine level may increase your risk for CAD and heart attack. Increasing your intake of folate (as well as vitamin B6 and vitamin B12) by eating more fruits and vegetables or taking supplements may reduce homocysteine levels (however, this measure is not proven to reduce cardiovascular risk).
- An elevated level of CRP indicates an increased amount of systemic inflammation, which may heighten your risk of CAD. Your doctor may recommend an aspirin a day to reduce your risk of a heart attack.
- Elevated levels of cardiac enzymes indicate that you are experiencing or have recently suffered a heart attack. However, because these enzymes are present in many organs and levels may be increased by a number of disease states, positive test results must be correlated to your physical signs and symptoms in order to confirm a heart attack. Treatment will be administered,
The Johns Hopkins Consumer Guide to Medical Tests
Simeon Margolis, M.D., Ph.D., Medical Editor
Updated by Remedy Health Media