Test Overview

A homocysteine test measures the amount of the amino acid homocysteine in the blood. You may have high levels of homocysteine when cholesterol, white blood cells, calcium, and other substances (plaque) build up in your blood vessels. This buildup may increase your chances of having a heart attack, stroke, and blood clots in the lungs (pulmonary embolism) or deep veins of the legs (deep venous thrombosis).

Homocysteine testing may be most useful in checking the overall risk of heart disease for people who have a strong personal or family history of heart disease but who do not have other risk factors that can be controlled, such as smoking or high blood pressure. Homocysteine testing also may be useful for people who have early heart disease but who do not have known risk factors and for people who have had unexplained deep vein thrombosis or stroke.

Why It Is Done

A homocysteine blood test is done to:

• Help determine your risk for having heart disease, stroke, and diseases of the blood vessels (peripheral arterial disease).
• Help identify vitamin B12 deficiency or folic acid deficiency. But other tests for these deficiencies are available.
• Help identify a rare inherited disease (homocystinuria) that causes a deficiency of one of several enzymes needed to convert food to energy.
• Help determine a cause for otherwise unexplained blood clots.

How To Prepare

Do not eat or drink anything (other than water) for at least 8 hours before the 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 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 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.

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.

Risks

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.
• Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin) and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

Results

A homocysteine test measures the amount of the amino acid homocysteine in the blood.

Results are ready in 24 hours.

Normal

Normal values may vary from lab to lab.

Many conditions can affect homocysteine levels. Your doctor will discuss any significant abnormal results with you in relation to your symptoms and medical history.

High values

High values of homocysteine may be caused by:

• Not getting enough folic acid, vitamin B6, or vitamin B12 in your diet.
• Other conditions or diseases, such as homocystinuria, kidney disease, hypothyroidism, Alzheimer's disease, or certain cancers.
• Using too much alcohol.
• Your sex. Homocysteine levels are normally higher in men than in women.
• Age. Homocysteine levels get higher as you get older.

Low values

Low values of homocysteine may be caused by some medicines or vitamins such as daily folic acid, vitamin B12, or niacin.

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

• Going through menopause.
• Having high blood pressure (hypertension).
• Smoking or other tobacco use.
• Having a family history of high homocysteine levels.
• Drinking more than 2 to 3 cups of coffee a day over many years.
• Taking medicines, such as anticonvulsants, antibiotics, theophylline, birth control pills, and tamoxifen.
• Having kidney disease, certain forms of leukemia, or psoriasis.
• Having a rare family (inherited) disease that causes the lack of an enzyme needed to prevent the build up of homocysteine in the blood (homocystinuria).

What To Think About

• A urine test may be done to help detect and monitor homocystinuria. But a blood test is more accurate.
• Homocysteine testing may be most valuable in evaluating the overall risk of heart disease for people who have a strong personal or family history of heart disease but who do not have other risk factors that can be controlled, such as smoking or high blood pressure.
• It is unclear whether elevated homocysteine levels alone increase your risk of heart disease. Your overall risk factors for heart disease must be evaluated along with your homocysteine levels. The relationship between homocysteine and cardiovascular disease is being studied in clinical trials.
• Vitamin B and folic acid supplements, which can lower homocysteine levels, do not lower the risk of a heart attack or stroke.¹ Most doctors recommend that you get B vitamins from a balanced diet, and they do not advise that you take vitamin B supplements.
• For more information on folic acid and vitamin B12, see the medical tests Folic Acid and Vitamin B12.