Homocysteine
The Test
How is it used?
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. Its utility for this purpose, however, continues to be questioned because the role, if any, that homocysteine plays in the progression of cardiovascular disease (CVD) has not been established. Routine screening, such as that done for total cholesterol, is not yet recommended.
When is it ordered?
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.
What does the test result mean?
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 stops short of calling 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 homocysteine levels in the highest 25% as compared to those in the lowest 25%.
Is there anything else I should know?
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.
