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Test Overview

A homocysteine test measures the amount of the amino acid homocysteine in the blood.

Why It Is Done

A homocysteine blood test is done to:

  • Help identify vitamin B12 deficiency or folic acid deficiency. But other tests for these deficiencies are available.
  • Help identify a rare inherited disease (homocystinuria) that causes a deficiency of one of several enzymes needed to convert food to energy.
  • Help determine a cause for otherwise unexplained blood clots.

How To Prepare

Do not eat or drink anything (other than water) for at least 8 hours before the test.

Many medicines may affect the results of this test. Be sure to tell your doctor about all the non-prescription and prescription medicines you take.

Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form .

How It Is Done

The health professional drawing your blood will:

  • Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
  • Clean the needle site with alcohol.
  • Put the needle into the vein. More than one needle stick may be needed.
  • Attach a tube to the needle to fill it with blood.
  • Remove the band from your arm when enough blood is collected.
  • Put a gauze pad or cotton ball over the needle site as the needle is removed.
  • Put pressure on the site and then put on a bandage.

How It Feels

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.


There is very little chance of a problem from having a blood sample taken from a vein.

  • You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
  • In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.


A homocysteine test measures the amount of the amino acid homocysteine in the blood.

Results are ready in 24 hours.


The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

Homocysteinefootnote 1


0.54–2.3 mg/L

4–17 micromoles per litre (mcmol/L)

Many conditions can affect homocysteine levels. Your doctor will discuss any significant abnormal results with you in relation to your symptoms and past health.

High values

High values of homocysteine may be caused by:

  • Not getting enough folic acid, vitamin B6, or vitamin B12 in your diet.
  • Other conditions or diseases, such as homocystinuria, kidney disease, hypothyroidism, Alzheimer's disease, or certain cancers.
  • Using too much alcohol.
  • Your sex. Homocysteine levels are normally higher in men than in women.
  • Age. Homocysteine levels get higher as you get older.

Low values

Low values of homocysteine may be caused by some medicines or vitamins such as daily folic acid, vitamin B12, or niacin.

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

  • Going through menopause.
  • Having high blood pressure (hypertension).
  • Smoking or other tobacco use.
  • Having a family history of high homocysteine levels.
  • Drinking more than 2 to 3 cups of coffee a day over many years.
  • Taking medicines, such as anticonvulsants, antibiotics, and birth control pills.
  • Having kidney disease, certain forms of leukemia, or psoriasis.
  • Having a rare family (inherited) disease that causes the lack of an enzyme needed to prevent the buildup of homocysteine in the blood (homocystinuria).



  1. Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.


Current as of: May 14, 2023

Author: Healthwise Staff
Clinical Review Board
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