Homocysteine
At a Glance
Why Get Tested?
To find out if you are at high risk of a heart attack or stroke; also used to determine if you are folate-deficient or vitamin B12-deficient as blood homocysteine concentration can be raised in both conditions
When to Get Tested?
If you have had a heart attack or stroke, particularly in the absence of traditional risk factors or as part of a cardiac risk assessment
Sample Required?
A blood sample taken by needle from a vein in the arm
The Test Sample
What is being tested?
This test measures the level of homocysteine in the blood. Homocysteine is a sulphur-containing amino acid that is normally present in very small amounts in all cells of the body. Homocysteine is a product of methionine metabolism, and methionine is one of the eleven “essential” amino acids (an essential amino acids must be derived from the diet since the body cannot make them). In healthy cells, homocysteine is quickly converted to other products.
Folic acid (folate) is one of the "B" vitamins that is needed to metabolise homocysteine. Vitamin B12, another B vitamin, helps keep folate in its active form, allowing it to keep homocysteine levels low. People who are deficient in these vitamins may have increased levels of homocysteine.
How is the sample collected for testing?
A blood sample is taken by needle from a vein in your arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
The Test
How is it used?
Homocysteine is now beginning to be used to help in the investigation of people who might be at high risk for heart attack or stroke. For example, it may be useful in patients who have a family history of coronary heart disease (CHD) but no other known risk factors.
The role of homocysteine for this purpose is however controversial because the role, if any, that it plays in the progression of CHD has not been established. While some evidence suggests that excess homocysteine may promote atherosclerosis by damaging blood vessel walls and supporting the formation of blood clots, there is not a direct link between the two and a number of studies have indicated no benefit or reduction in CVD risk with folic acid and B vitamin supplementation.
There are, as of yet, no established guidelines for homocysteine testing, and routine screening is not recommended.
Occasionally, a doctor may also request a homocysteine test in the investigation of suspected vitamin B12 or folate deficiency.
When is it requested?
Homocysteine may be requested as part of a cardiac risk assessment, depending on your age and other risk factors. It may also be used following a heart attack or stroke to help determine treatment.
What does the test result mean?
At present, a direct correlation between homocysteine levels and heart attacks has not been established, but there does seem to be strong evidence of a relationship between homocysteine levels and heart attack/stroke survival rates.
While earlier studies suggested that people who have elevated homocysteine levels have a much greater risk of heart attack or stroke than those with average levels, at present, the use of homocysteine levels for risk assessment of cardiovascular disease (CVD), peripheral vascular disease and stroke is uncertain given that several trials investigating folic acid and B vitamin supplementation indicate no benefit or lowering of CVD risk. Since measuring homocysteine levels to determine cardiac risk is a relatively new use for the test, the exact reference range has yet to be determined.
Is there anything else I should know?
There is a hereditary (genetic) form of homocystinuria – an increase of homocysteine in the urine – that causes a form of mental retardation, skeletal abnormalities, and premature cardiovascular disease. A gene mutation prevents an enzyme from breaking down homocysteine into products that can be excreted through the kidneys. The build-up of homocysteine can become toxic to the body. The most common hereditary form results in both an increase in homocysteine and a decrease in folic acid.
Homocysteine levels can increase with age, when a patient smokes, and with the use of drugs such as carbamazepine, methotrexate, and phenytoin. Homocysteine levels are lower in women than in men. Women’s concentrations increase after menopause, possibly due to decreased estrogen production.
Common Questions
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Article Sources
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
