Homocysteine – laboratory test

Description

Why homocysteine is tested

Homocysteine is an amino acid produced in the body from methionine. Under normal conditions, it is quickly metabolised with the help of vitamins B12, B6 and folic acid. When these are deficient or metabolism is impaired by a genetic condition, homocysteine accumulates in the blood and damages the lining of blood vessels. Elevated levels are associated with a higher risk of atherosclerosis, heart attack, ischaemic stroke and venous thrombosis.

In practice, the test has two main uses: as a sensitive marker of vitamin B12 and folate deficiency (a normal fasting result largely rules out B12 deficiency), and as an additional indicator of cardiovascular risk in people whose disease is not explained by conventional risk factors.

When to consider this test

• after a heart attack, stroke or thrombosis, especially at a young age or without typical risk factors,
• if there is a family history of cardiovascular disease with an unclear cause,
• if vitamin B12 or folic acid deficiency is suspected (anaemia, fatigue, numbness, a vegan diet),
• in people with an MTHFR polymorphism or suspected homocystinuria,
• when planning a pregnancy and during pregnancy, when a doctor is assessing the risk of hypertension and neural tube defects,
• in chronic kidney disease, hypothyroidism, or during treatment with methotrexate, phenytoin, carbamazepine or fibrates.

How to prepare

• Fast: have your last meal at least 8 hours before the blood sample is taken; you may drink water in the morning.
• The day before, avoid large amounts of protein (methionine can increase the result by up to approximately 15%), alcohol and strong coffee; do not smoke in the morning.
• If you take supplements containing B12, folic acid, B6 or S-adenosylmethionine (SAMe), make a note of this and show it to your doctor when discussing the result; do not stop taking medication without consulting your doctor.
• Important when choosing a collection point: blood for homocysteine testing must be cooled immediately and centrifuged within an hour; otherwise, the level rises in the tube itself. This is why the test is only available at collection points located at laboratories. When choosing a location in your basket, you will only see these collection points.

Understanding your result

The result is reported in µmol/l. The reference range depends on age, sex and the laboratory: in adults, the upper limit is usually between approximately 10 and 16 µmol/l (it increases with age and is slightly higher in men). Always compare your result with the range shown on your report.

Elevated homocysteine is not a diagnosis, but a warning sign. The most common cause, B12 or folate deficiency, can be corrected through diet and supplementation, with a repeat test after 2–3 months.

What to test alongside homocysteine

Doctors most often request it together with: vitamin B12, folic acid, a lipid profile and creatinine. More about the test and how to interpret it: Badania-Medyczne.pl.

Sources: Diagnostyka, “Homocysteine” leaflet (preparation, sample handling, causes); Mayo Clinic Laboratories, HCYSP test (age- and sex-specific ranges, sample stability). This information does not replace a medical consultation.