Homocysteine test: what the result means
- Updated
- 2026-09-10
- Every number with its source
What homocysteine is and what the test shows
Homocysteine is an amino acid that is formed when the body breaks down the protein methionine. In a healthy person's body homocysteine is quickly processed further — vitamins B6, B12 and folic acid are needed for this process. When these vitamins are lacking, or when the enzymes that regulate their metabolism are disturbed, homocysteine builds up in the blood. Per MedlinePlus, a raised homocysteine level may be linked with an insufficient amount of vitamin B12 or folic acid in the diet, and it can also indicate a rare inherited condition — homocystinuria. The test is also used to assess people who are at higher risk of cardiovascular disease, because MedlinePlus states that a higher homocysteine level is linked with a higher risk of heart disease, stroke and other vascular disorders. A homocysteine test is often ordered together with vitamin B12 and folic acid tests, so that it is clear whether the rise is caused by a vitamin deficiency.
When homocysteine is tested
- To assess the amount of vitamins B6, B12 and folic acid in the body
- When a rare inherited condition — homocystinuria — is suspected
- To assess the risk of cardiovascular disease in people whose risk is already raised for other reasons
- To monitor people with a family history of early heart disease or stroke
- When looking into the causes of unexplained tiredness or other symptoms linked with a vitamin deficiency
How to prepare
- You may need to avoid food and drink for 8–12 hours before the test
- Tell your doctor about all the medicines and food supplements you take, especially B-group vitamin supplements, because they can affect the result
The exact instruction is given by your own doctor or laboratory; see also how to prepare for a blood test.
Reference range
MedlinePlus does not currently give a general numeric reference interval, because reference limits depend on the laboratory's method. You will find your laboratory's exact interval on your own result sheet — it is worth discussing with your doctor together with your vitamin B12 and folic acid results. See also how to read blood test results.
A raised homocysteine result
A raised homocysteine level may indicate an insufficient amount of vitamin B12 or folic acid in the diet. A rare cause is inherited homocystinuria. Per MedlinePlus, a higher homocysteine level is linked with a higher risk of heart disease, stroke and other vascular disorders, and also with osteoporosis, chronic kidney disease, hypothyroidism and some diseases of the nervous system.
Causes listed for a raised result:
- An insufficient amount of vitamin B12 or folic acid in the diet
- Homocystinuria — a rare inherited metabolic disease
- Chronic kidney disease
- Hypothyroidism (reduced thyroid function)
- Smoking
- Age and sex can influence the result
What is usually looked at after a raised result:
- Vitamin B12 and folic acid tests — so that it is clear whether the rise is caused by a vitamin deficiency
- Thyroid function and kidney markers
- Family history of early heart disease or stroke
- Discuss with your doctor whether a broader assessment of cardiovascular risk is needed
Related pages
Related pages on this site: vitamin B12, folic acid, cholesterol, CRP, hs-CRP, creatinine.
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Frequently asked questions
›What is the normal homocysteine level in blood?
MedlinePlus does not currently give a general numeric reference interval, because reference limits depend on the laboratory's method. You will find your laboratory's exact interval on your own result sheet — it is worth discussing with your doctor together with your vitamin B12 and folic acid results.
›Why is a homocysteine test done?
Per MedlinePlus, the test is used first of all to assess the amount of vitamins B6, B12 and folic acid in the body, and also to diagnose the rare inherited condition homocystinuria and to assess the risk of cardiovascular disease in people whose risk is already raised.
›Why can homocysteine be raised?
A possible cause is an insufficient amount of vitamin B12 or folic acid in the diet. The rise can also be caused by rare inherited homocystinuria, chronic kidney disease, hypothyroidism or smoking. Vitamin B12 and folic acid tests help to work out the cause.
›Is a raised homocysteine level linked with heart disease?
MedlinePlus states that a higher homocysteine level is linked with a higher risk of heart disease, stroke and other vascular disorders, but this does not mean a diagnosis — the result needs to be discussed with your doctor together with your other risk factors.
›Do I need to avoid eating before a homocysteine test?
Per MedlinePlus, you may need to avoid food and drink for 8–12 hours before the test. It is also worth telling your doctor about the medicines and food supplements you take, especially B-group vitamin supplements.
›What is homocystinuria?
Homocystinuria is a rare inherited metabolic disease in which the body cannot process homocysteine properly, so its amount in the blood rises sharply. The homocysteine test is used to diagnose this condition.
Sources
Related markers
This site is not an emergency service. If severe chest or head pain, breathlessness, confusion, difficulty speaking, heavy bleeding or another acute problem has come on suddenly — do not wait for tests, call 112.
This information is not a diagnosis and does not replace a consultation with a doctor. Reference ranges depend on the laboratory, your age and sex — always compare your result with the range printed on your own report.