Home › Biomarkers › Homocysteine
Homocysteine is an amino acid in your blood. Normally the level is low. A high level can point to a shortage of certain B vitamins, or to homocysteine not being broken down properly.[1]
On this page you can read what homocysteine is, what the guidelines say about a level that is too low or too high, what affects your level and which other values are best to look at alongside it.
Also known as: total homocysteine, total plasma homocysteine. At the lab: HOCY.
Homocysteine is an amino acid. Amino acids are substances your body uses to make proteins. The test measures how much homocysteine is in your blood.[1]
Normally your level is low. Your body uses vitamin B12, vitamin B6 and folic acid (also called folate or vitamin B9) to break homocysteine down quickly. This way it turns homocysteine into other substances it needs.[1]
An international group of experts describes how a higher level goes together with many different conditions. That is why homocysteine is measured both in healthcare and in research.[2]
A high level can be a sign that homocysteine is not being broken down properly, or that you are short of certain B vitamins. That is why the test is mainly used to get a picture of your vitamin B6, B12 and folic acid.[1]
Too little of these vitamins can lead to anaemia, damage to nerves throughout your body and a decline in your memory and thinking.[1]
If homocysteine is not broken down, it can build up in your arteries. That can damage your arteries and raise the chance of blood clots. This can also raise your risk of heart and blood vessel disease.[1]
Even so, testing everyone for this value as standard is not recommended. It is uncertain how much homocysteine plays a part in conditions of the heart and blood vessels. In most cases, a lower value does not reduce that risk.[1]
Labplusarts, the lab BioProfile works with, uses a reference value for homocysteine of 5 to 13 μmol/L, measured fasting. The lab calls a level between those limits normal.[3]
| Value | What it can mean | Who it is for |
|---|---|---|
| 5 to 13 μmol/L[3] | The lab calls this value normal | When measured fasting |
Source: Labplusarts, the lab's reference value for homocysteine (HOCY), measured fasting.[3]
A high level can point to too little vitamin B12 or folic acid in your diet. It can also point to a rare inherited metabolic condition, or to a higher risk of heart and blood vessel disease. A higher level is also seen with other conditions, for example of the bones, kidneys, thyroid or brain. A high level does not always mean there is a condition that needs care. Talk through your result with a doctor.[1]
BioProfile is working on its own zones for each value, from risk to optimal. A doctor reviews those zones before they appear in your result.
Your level can rise as you get older. Men usually have a higher level than women. In women, though, the level does rise after the menopause.[1]
Smoking also plays a part in your result.[1]
Sometimes you need to fast for 8 to 12 hours before the test. Some medicines and supplements can change your result, especially vitamin B. Tell your doctor which ones you take. Do not stop taking any medicine on your own.[1]
An international group of experts names the taking and processing of the blood sample, factors within your own body and the way the level varies within the same person as points that matter when measuring homocysteine.[2]
Homocysteine is included in BioProfile 150.[4]
The BioProfile editorial team wrote this page on 10 October 2026 from the sources below, which we read on 10 October 2026. Every number on this page appears in one of those sources, with that source's number next to it. An expert has yet to check this page; after that check, the expert's name and the date of the check will appear at the top. This page offers explanation, not a diagnosis. Discuss a value outside the range with your GP.
