Also Known As
Plasma Total Homocysteine
Urine Homocysteine
This article was last reviewed on
This article waslast modified on 31 January 2022.
At a Glance
Why Get Tested?

To find out if you have a rare inborn error of metabolism (homcystinuria); 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 symptoms consistent with homocystinuria, for example dislocation of the lens of the eye or some blood clots, and all newborn babies are tested via heel prick in the newborn screening program. Rarely when vitamin B12 concentrations are borderline and suspicion is high that B12 deficiency is present homocysteine (or methylmalonic acid) can help prove tissue deficiency in the face of a normal blood concentration.

Sample Required?

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

Test Preparation Needed?

You may be instructed to fast for 10 to 12 hours prior to this test

On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

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 produced when methionine is metabolised, 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.

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Common Questions
  • How is it used?

    Homocysteine can be used to detect homocystinuria. The amino acid concentrations of methionine and homocysteine are measured in the blood, and sometimes urine, including in the blood spot from a newborn baby’s heel to detect and screen for this condition.

    Occasionally, a doctor may also request a homocysteine test in the investigation of suspected vitamin B12 or folate deficiency.

  • When is it requested?

    Homocysteine is measured in all newborns in the UK who are tested as part of the newborn screening program. People affected with suspected homocystinuria and relatives may also be tested.

  • What does the test result mean?

    A high levels may infer vitamin deficiency or, very rarely, homocystinuria however many other factors can cause it to, for example kidney disease or a non-fasting specimen.

  • Is there anything else I should know?

    There is evidence of an association between homocysteine levels and cardiovascular disease e.g. heart attack/stroke. However reduction of homocysteine levels with B vitamins does not reduce the risk therefore there is no evidence that the homocysteine is causing the problem. Therefore measurement of homocysteine to asses cardiovascular risk, and treatment with folic acid for example, is not standard recommended care.

    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 oestrogen production.

    Homocystinuria is a rare inherited metabolic disorder characterised by an increased blood and urine concentration of homocysteine. Classical homocystinuria is due to a deficiency in cystathionine beta synthase (CBS). Affected individuals appear normal at birth but develop serious complications in childhood. Diagnosis and treatment started sufficiently early in life can effectively prevent or reduce the severity of these complications.

  • What are some good sources of folic acid and vitamins B6 and B12?

    Green leafy vegetables and cereal grains are the main source of folic acid. Fruits and vegetables have significant amounts of vitamin B6, and vitamin B12 can be found in red meats, poultry, fish, and other seafoods.

  • Could any drugs I may be taking have an effect on my homocysteine level?

    Yes. There are numerous drugs that may either increase or decrease the amount of homocysteine in your body. You should always keep your doctor and pharmacist aware of any drugs, traditional or herbal, you are taking, since they may interfere with the test results.

  • Could any drugs I may be taking have an effect on my homocysteine level?

    Yes. There are numerous drugs that may either increase or decrease the amount of homocysteine in your body. You should always keep your doctor and pharmacist aware of any drugs, traditional or herbal, you are taking, since they may interfere with the test results.

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