Homocysteine Test

A homocysteine test measures the amount of homocysteine in a sample of your blood. Homocysteine is an amino acid. Amino acids are molecules that your body uses to make proteins.

Normally, your homocysteine levels are low. That's because your body uses vitamin B12, vitamin B6, and folic acid (also called folate or vitamin B9) to quickly break down homocysteine and change it into other substances that your body needs. High levels of homocysteine in your blood may be a sign that this process isn't working right or that you're lacking certain B vitamins.

If homocysteine isn't broken down, it can build up in your arteries (blood vessels that carry oxygen-rich blood from your heart and lungs to your body). This can not only damage your arteries but also increase your risk of forming blood clots. An increased risk of forming blood clots may increase your risk for heart attack, stroke, and other heart diseases and blood vessel disorders.

Why this test is done

You may need this test if you are at high risk for low levels of vitamin B12 or folic acid or if you have symptoms that suggest you lack either of these vitamins. The symptoms may be very mild to severe and may include:

• Dizziness.
• Fatigue and/or weakness.
• Headache.
• Heart palpitations (racing or pounding heart).
• Changes in the color of your skin or fingernails.
• Sores on your tongue or in your mouth.
• Tingling or numbness in your hands, feet, arms, and/or legs.

You may be at high risk for low levels of vitamin B12 or folic acid if you:

• Have malnutrition.
• Are an older adult. Older people often can't absorb enough vitamin B12 from food.
• Have alcohol use disorder or a drug addiction.

Your provider may also recommend this test if you have:

• Had a heart attack or stroke.
• One or more conditions that increase your risk for heart attack or stroke, such as high LDL "bad" cholesterol or high blood pressure.
• Homocystinuria. Because this condition makes the breakdown of homocysteine difficult, you are more likely to have high levels of this amino acid.

How to prepare

You may need to fast (not eat or drink) for 8-12 hours before a homocysteine test. Some medicines and supplements may affect your test results. So, tell your provider about all medicines and supplements you take, especially vitamin B.

But don't stop taking any medicines unless your provider tells you to.

Sample type

Blood

Other names for this test

total homocysteine, plasma total homocysteine