Homocysteine
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- Also Known As:
- Plasma Total Homocysteine
- Urine Homocysteine
- Homocysteine Cardiac Risk

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At a Glance
Why Get Tested?
To help determine if you are deficient in vitamins B6, B9 (folate) or B12; to determine if you are at increased risk of heart attack or stroke; to monitor those who have heart disease; sometimes to help diagnose a rare inherited disorder called homocystinuria in newborns
When To Get Tested?
When your health care provider suspects that you have a vitamin B6, B12 or folate deficiency; when you have had a heart attack or stroke and do not have traditional risk factors, such as unhealthy lipid levels
Sample Required?
A blood sample taken by needle from a vein
Test Preparation Needed?
You may be instructed to fast for 10 to 12 hours prior to this test; only water is permitted.
You may be able to find your test results on your laboratory’s website or patient portal. However, you are currently at Testing.com. You may have been directed here by your lab’s website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab’s website or portal, or contact your healthcare practitioner in order to obtain your test results.
Testing.com is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.
The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.
If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.
Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called “normal” values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.
While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are “within normal limits.”
For more information, please read the article Reference Ranges and What They Mean.
What is being tested?
Homocysteine is an amino acid that is typically present in very small amounts in all cells of the body. That is because the body normally converts homocysteine into other products quickly. Since vitamins B6, B12, and folate are necessary to metabolize homocysteine, increased levels of the amino acid may be a sign of deficiency in those vitamins. This test determines the level of homocysteine in the blood and/or urine.
Elevated homocysteine may also be related to a higher risk for coronary heart disease, stroke, peripheral vascular disease (fatty deposits in peripheral arteries), and hardening of the arteries (atherosclerosis). High levels of homocysteine increase the risk of blood clot formation in vessels and may lead to heart attack and stroke. Several mechanisms have been proposed for how homocysteine leads to cardiovascular disease (CVD) risk, but direct links haven not been confirmed. There are also several studies that indicate no benefit or lowering of CVD risk with folic acid and B vitamin supplements. So far, the American Heart Association does not consider it a major risk factor for heart disease.
A rare inherited condition called homocystinuria can also greatly increase homocysteine in the blood and urine. In the U.S., all babies are routinely tested for excess methionine, a sign of homocystinuria, as part of their newborn screening. If a baby’s screening test is positive, then urine and blood homocysteine tests are often performed.
Common Questions
View Sources
Sources Used in Current Review
Homocysteine Test. MedlinePlus. Available online at https://medlineplus.gov/labtests/homocysteinetest.html. Accessed on 8/28/18.
(July 7, 2015) Homocysteine and MTHFR Mutations. Circulation. Available online at https://www.ahajournals.org/doi/abs/10.1161/circulationaha.114.013311. Accessed on 8/28/18.
(2002) Emergent Cardiovascular Risk Factor: Homocysteine. Progress in Cardiovascular Nursing. Available online at https://www.medscape.com/viewarticle/431273_4. Accessed on 8/28/18.
Three of the B Vitamins: Folate, Vitamin B6, and Vitamin B12. Harvard T.H. Chan School of Public Health. Available online at https://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/vitamins/vitamin-b/. Accessed on 8/28/18.
(March 2016) Homocystinuria. Genetics Home Reference. U.S. National Library of Medicine. Available online at https://ghr.nlm.nih.gov/condition/homocystinuria#sourcesforpage. Accessed on 8/28/18.
(January 10, 2015) Role of homocysteine in the development of cardiovascular disease. Nutrition Journal. Available online at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4326479/. Accessed on 8/28/18.
Sources Used in Previous Review
Thomas, Clayton L., Editor (1997). Taber’s Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby’s Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO. Pp 488-490.
Stewart. D. (2004 July 26, Updated). Homocystinuria. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/001199.htm.
Picker, J. and Levy, H. (2005 August 15, Updated). Homocystinuria Caused by Cystathionine Beta-Synthase Deficiency. GeneReviews [On-line information]. Available online at http://www.genetests.org/query?dz=homocystinuria.
(2005 September 23) Homocystinuria. Genetics Home Reference, Homocystinuria [On-line information]. Available online at http://ghr.nlm.nih.gov/condition=homocystinuria.
Genetic Fact Sheets for Parents, Amino Acid Disorders. Expanded Newborn Screening with Tandem Mass Spectrometry Financial, Ethical, Legal, and Social Issues [On-line information]. Available online at http://www.newbornscreening.info/Parents/aminoaciddisorders/CBS.html.
(2005 May 02, Reviewed). Genetic Fact Sheets for Professionals, Amino Acid Disorders. Expanded Newborn Screening with Tandem Mass Spectrometry Financial, Ethical, Legal, and Social Issues [On-line information]. Available online at http://www.newbornscreening.info/Pro/aminoaciddisorders/CBS.html.
Homocysteine May Trigger Strokes. JS Online. Available online at http://www.jsonline.com/alive/ap/feb01/ap-stroke-amino-ac021601.asp.
Homocysteine: An emerging age-related cardiovascular risk factor. Geriatrics. April 1999.
Donald W. Jacobsen, PhD, FAHA. Director, Laboratory for Homocysteine Research, Department of Cell Biology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH. (Fellow, American Heart Association; American Association for Clinical Chemistry member).
Pagana, K. D. & Pagana, T. J. (© 2007). Mosby’s Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 541-543.
Clarke, W. and Dufour, D. R., Editors (© 2006). Contemporary Practice in Clinical Chemistry: AACC Press, Washington, DC. Pp 434-435.
Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pp 574-577.
What Is Homocysteine? American Heart Association [On-line information]. Available online at http://www.americanheart.org/presenter.jhtml?identifier=535. Accessed May 2009.
(Updated 2008 July). Familydoctor.org. [On-line information] Available online at http://familydoctor.org/online/famdocen/home/articles/249.html. Accessed May 2009.
(2008 January). Homocystinuria. Genetics Home Reference [On-line information]. Available online at http://ghr.nlm.nih.gov/condition=homocystinuria. Accessed May 2009.
(© 2009). Homocysteine, Folic Acid and Cardiovascular Disease. American Heart Association [On-line information]. Available online at http://www.americanheart.org/presenter.jhtml?identifier=4677. Accessed May 2009.
Baloghova, J. et. al. (2006 December 6). Homocystinuria. emedicine [On-line information]. Available online at http://emedicine.medscape.com/article/1115062-overview. Accessed May 2009.
(Updated 2008 December). Cardiovascular Disease (Non-traditional Risk Markers) – Risk Markers – CVD (Non-traditional). ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/CardiacDz/CVDRiskMarkerNontrad.html. Accessed May 2009.
National Academy of Clinical Biochemistry. Laboratory Medicine Practice Guidelines: Emerging Biomarkers for Primary Prevention of Cardiovascular Disease and Stroke (2009) Homocysteine and Cardiovascular Disease Risk. Pg. 51. PDF available for download at http://www.aacc.org/members/nacb/LMPG/OnlineGuide/PublishedGuidelines/risk/Documents/PublishedGuidelines.pdf.
Clarke R, Bennett DA, Parish S, Verhoef P, Dötsch-Klerk M, et al. (2012) Homocysteine and Coronary Heart Disease: Meta-analysis of MTHFR Case-Control Studies, Avoiding Publication Bias. PLoS Med 9(2): e1001177. doi:10.1371/journal.pmed.1001177. Accessed February 2014.
Pagana, K. D. & Pagana, T. J. (© 2013). Mosby’s Diagnostic and Laboratory Test Reference 11th Edition: Mosby, Inc., Saint Louis, MO. Pp 537-538.
(Updated Feburary 2012). Homocystinuria. MedlinePlus Medical Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/001199.htm. Accessed February 2014.
(Updated 2010 July). Coronary Artery Disease | High Homocysteine Level: How It Affects Your Blood Vessels. Familydoctor.org. Available online at http://familydoctor.org/online/famdocen/home/articles/249.html. Accessed February 2014.
(Reviewed 2011 July). Homocystinuria. Genetics Home Reference. Available online at http://ghr.nlm.nih.gov/condition=homocystinuria. Accessed February 2014.
(Updated 20 January 2012). Homocysteine, Folic Acid and Cardiovascular Disease. American Heart Association. Available online through http://www.americanheart.org. Accessed February 2014.
Mandava P. et al. (Updated 2013 June 20). Homocystinuria/Homocysteinemia. Medscape Available online at http://emedicine.medscape.com/article/1952251-overview#a30. Accessed February 2014.
Baloghova, J. et. al. (Upated 2013 July 24). Dermetologic Manifestations of Homocystinuria. Medscape. Available online at http://emedicine.medscape.com/article/1115062-overview. Accessed February 2014.
(Updated January 6, 2013) National Newborn Screening and Genetics Resource Center. National Newborn Screening Status Report. Available online at http://genes-r-us.uthscsa.edu/sites/genes-r-us/files/nbsdisorders.pdf. Accessed February 2014.
(Updated May 26, 2013) The Screening, Technology And Research in Genetics (STAR-G) Project, Homocystinuria Factsheet. Available online at http://www.newbornscreening.info/Parents/aminoaciddisorders/CBS.html. Accessed February 2014.
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