Also known as: Total plasma homocysteine
Name: Homocysteine
Related tests: Cardiovascular risk assessment, Total cholesterol, Folic acid, Vitamin B12
Why is the test done?
To assess whether you are at increased cardiovascular risk; homocysteine can also be useful in vitamin B12 or folate deficiency. In a rare inherited disease, homocystinuria, homocysteine can be very useful for diagnosis.
When is the test done?
In the assessment of overall cardiovascular risk or after previous cardiovascular disease, and when homocystinuria or vitamin B12 or folate deficiency is suspected.
What samples are required?
A blood sample from a vein. In rare cases a urine sample may be needed as well as the blood sample.
What is being analysed?
This test measures homocysteine in plasma or urine. Homocysteine is a sulphur-containing amino acid derived from the metabolism of methionine, one of the essential amino acids; normally the homocysteine produced inside cells is rapidly metabolised and converted into other products; vitamins B6 and B12 and folate are essential for these processes, and a deficiency of these vitamins can raise plasma homocysteine.
Recent studies suggest that high plasma homocysteine levels are associated with increased cardiovascular risk; how homocysteine acts is not yet clear, but it seems to be linked to changes in clotting and damage to the lining of the blood vessels.
People with homocystinuria, a rare inherited disease, have very high homocysteine values. This disorder can be caused by mutations in different genes and prevents methionine and homocysteine from being metabolised, so they build up in the plasma. An affected person may be normal at birth, but at the age of 3-5 the first clinical signs appear, including dislocation of the lens of the eye, learning disability, skeletal abnormalities, osteoporosis and an increased risk of thromboembolism and atherosclerosis.
How is the sample collected for testing?
The sample is taken from a vein in the arm. In rare cases a urine sample may need to be collected as well as the blood sample.
How is it used?
When is it requested?
What does the test result mean?
Is there anything else I should know?
How is it used?
Homocysteine is generally used to assess cardiovascular risk together with other parameters such as the lipid profile, or when there are other risk factors such as a family history of heart disease. Nevertheless, the usefulness of homocysteine in determining cardiovascular risk is still debated, as the role of this amino acid in the progression of cardiovascular disease has not yet been clearly defined. The homocysteine test cannot be used for screening in the way other tests, such as the lipid profile, are.
The doctor may also request homocysteine to assess a possible vitamin B12 or folate deficiency: this often happens in malnourished patients, in elderly people, who may have reduced absorption from the gut, in alcoholics and in drug users.
Homocysteine may also be requested when homocystinuria is suspected.
Treatment of hyperhomocysteinaemia can be monitored by repeating the homocysteine test periodically.
When is it requested?
Most often the homocysteine test is requested together with other tests to assess cardiovascular risk, taking into account the presence of other risk factors. This test may also be requested to check for vitamin B12 and folate deficiency and when homocystinuria is suspected.
What does the test result mean?
Recent studies suggest that high homocysteine values are associated with an increased risk of cardiovascular disease. A precise correlation between homocysteine and cardiovascular risk has not yet been established, so interpretation of the result for risk assessment is not yet standardised. In many cases plasma homocysteine can be lowered by taking vitamins B6 and B12 and folate; elderly people often have higher homocysteine values, and this type of supplement may be indicated.
Values well above the reference limit can be seen in children with homocystinuria; in this case further tests are needed to identify the cause of the increase.
Is there anything else I should know?
When homocystinuria is suspected, a liver biopsy and a genetic test for the most common mutations may be requested; if a family member has been diagnosed with homocystinuria, the patient must be tested for the mutation found in the affected relative.
Plasma homocysteine can rise with age, with smoking and during treatment with carbamazepine or methotrexate.
1. What are the dietary sources of vitamins B6 and B12 and folate?
2. Can hyperhomocysteinaemia affect cardiovascular risk differently in men and women?
3. Which medicines can affect plasma homocysteine levels?
1. What are the dietary sources of vitamins B6 and B12 and folate?
Cereals are the main source of folic acid; fruit and vegetables in general contain significant amounts of vitamin B6, while vitamin B12 is found mainly in red meat, poultry and fish. Plasma homocysteine levels can be lowered by taking multivitamin supplements.
2. Can hyperhomocysteinaemia affect the increase in cardiovascular risk differently in men and women?
Plasma homocysteine is higher in women after the menopause, possibly because of the lack of oestrogen; nevertheless, cardiovascular risk does not seem to increase because of this moderate rise.
3. Which medicines can affect plasma homocysteine levels?
Several medicines can raise homocysteine; you should always tell your doctor about any treatment you are having so that the test result can be interpreted correctly.