Homocysteine

Why Get Tested?

  • To determine if you are at increased risk of heart attack or stroke
  • To determine if you are folate-deficient or B12-deficient
  • To help diagnose a rare inherited disorder called homocystinurina

When to Get Tested?

When a doctor suspects a vitamin B12 or folate deficiency or suspects that an infant or young person may have homocystinuria; when you have had a heart attack or stroke and do not have traditional risk factors,
as part of a cardiac risk assessment

This test may be ordered when a doctor suspects that a person may have a B12 and/or folate deficiency or when a baby has signs or symptoms that suggest that he or she may have homocystinuria.

Homocysteine may be ordered as part of a cardiac risk assessment, depending on the patient’s age and other risk factors. It may also be ordered following a heart attack or stroke to help guide treatment.

Sample Required?

A blood sample taken by needle from a vein in the arm;

Test Preparation Needed?

No preparation is required.

What is being tested?

This test determines the level of homocysteine in the blood or urine. Homocysteine is a sulfur-containing amino acid that is normally present in very small amounts in all cells of the body. Homocysteine is a product of methionine metabolism. Methionine is one of the eleven “essential” amino acids – amino acids that must be derived from the diet since the body cannot produce them. In healthy cells, homocysteine is quickly converted to other products.

Vitamins B6, B12, and folate are necessary to metabolize homocysteine. People who are deficient in these vitamins may have increased levels of homocysteine.

According to the American Heart Association (AHA), some evidence suggests that excess homocysteine may promote atherosclerosis by damaging blood vessel walls and supporting the formation of inappropriate blood clots, but there is not a direct link between the two. The benefit of using homocysteine levels for risk assessment of cardiovascular disease (CVD), peripheral vascular disease, and stroke is uncertain given that several studies indicate no benefit or lowering of CVD risk with folic acid and B vitamin supplementation.

Homocysteine can be greatly increased in the blood and urine of people with a rare inherited condition called homocystinuria. This disorder is caused by an alteration in one of several different genes. The affected person has a dysfunctional enzyme that does not allow the normal breakdown of methionine. Because of this, homocysteine and methionine begin to build up in the person’s body. A baby with this condition will appear normal at birth but within a few years will begin to develop signs such as a dislocated lens in the eye, a long slender build, long thin fingers, skeletal abnormalities, osteoporosis, and a greatly increased risk of thromboembolism and of atherosclerosis that can lead to premature cardiovascular disease. The buildup may also cause progressive mental retardation, behavioral disorders, and seizures.

How is the sample collected for testing?

A blood sample is taken by needle from a vein in the arm; sometimes a urine sample is also collected.

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 AnxietyTips on Blood TestingTips 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.

How is it used?

A physician may order a homocysteine test to determine if a person has B12 or folate deficiency. The homocysteine concentration may be elevated before B12 and folate tests are abnormal. Some doctors may recommend homocysteine testing in malnourished patients, the elderly, who often absorb less vitamin B12 from their diets, and those with drug or alcohol addictions.

A doctor may order both a urine and blood homocysteine to help diagnose homocystinuria if she suspects that an infant may have this inherited disorder. In some states, babies are tested for excess methionine as part of their newborn screening. If a baby’s test is positive, then urine and blood homocysteine tests are often performed to confirm the findings.

Homocysteine may also be ordered as part of a screen for people at high risk for heart attack or stroke. It may be useful in someone who has a family history of coronary artery disease but no other known risk factors.

What does the test result mean?

In cases of suspected malnutrition or vitamin B12 or folate deficiency, homocysteine levels may be elevated. If you do not get enough B vitamins and/or folate through diet or supplements, then your body may not be able to convert homocysteine to forms that can be used by your body. In this case, levels of homocysteine in the blood can increase.

In newborn testing, greatly increased concentrations of homocysteine in the urine and blood mean that it is likely that an infant has homocystinuria and indicates the need for further testing to confirm the cause of the increase.

Older studies (1995 to 1999) 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, however, the use of homscysteine 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. The AHA does acknowledge strong evidence of a relationship between homocysteine levels and heart attack/stroke survival rates but calls elevated homocysteine a major risk factor for cardiovascular disease. Blockage of a coronary artery, a precursor to a heart attack, occurs with more than double the average frequency in people with raised homocysteine levels