Test Overview

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

Why It Is Done

homocysteine blood test is done to:

  • Help
    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 nonprescription and prescription medicines you take.

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 (What is a PDF document?).

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
  • Put the needle into the vein. More than one needle stick
    may be needed.
  • Attach a tube to the needle to fill it with
  • Remove the band from your arm when enough blood is
  • 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

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


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
  • 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
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

micromoles per liter (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:

Low values

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

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
  • 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
  • Having a rare family (inherited) disease that causes the lack of
    enzyme needed to prevent the buildup of homocysteine
    in the blood (homocystinuria).

What To Think About

  • A urine test may be done to help detect and
    monitor homocystinuria. But a blood test is more
  • Most
    doctors recommend that you get B vitamins from a balanced diet, and they do not
    advise that you take vitamin B supplements.



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

Other Works Consulted

  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
  • Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.


ByHealthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD – Internal Medicine
Adam Husney, MD – Family Medicine
Specialist Medical Reviewer Martin J. Gabica, MD – Family Medicine

Current as ofOctober 9, 2017