Vitamin B12 and Folate

Share this page:
Looking for your tests results? Looking for reference ranges?
Also known as: Cobalamin; Folic Acid; RBC Folate
Formal name: Vitamin B12; Folate

At a Glance

Why Get Tested?

To help diagnose one cause of anemia or neuropathy; to evaluate nutritional status in some people; to monitor the effectiveness of treatment for vitamin B12 or folate deficiency

When to Get Tested?

When you have an abnormal CBC with a blood smear showing large red blood cells (macrocytosis) or abnormal (hypersegmented) neutrophils; when you have symptoms of anemia (weakness, tiredness, pale skin) and/or of neuropathy (tingling or itching sensations, eye twitching, memory loss, altered mental status); when you are being treated for vitamin B12 or folate deficiency

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

Fasting for 6-8 hours before sample collection may be required.

The Test Sample

What is being tested?

Vitamin B12 and folate are both part of the B complex of vitamins. These tests measure the levels of folate and vitamin B12 in the liquid portion of the blood, the serum or plasma, to detect deficiencies. The amount of folate inside the red blood cell (RBC) may also be measured -- it will normally be at a higher concentration than serum or plasma folate.

Folate refers to a natural occurring form, whereas folic acid refers to the supplement added to foods and drinks. It is found in leafy green vegetables, citrus fruits, dry beans and peas, liver, and yeast. Cobalamine, or vitamin B12, is found in animal products such as red meat, fish, poultry, milk, yogurt, and eggs and is not produced in the human body. In recent years, fortified cereals, breads, and other grain products have also become important dietary sources of B12 and folate (identified as "folic acid" on nutritional labels).

Both B12 and folate are necessary for normal RBC formation, tissue and cellular repair, and DNA synthesis. B12 is important for nerve health, while folate is necessary for cell division such as is seen in a developing fetus. A deficiency in either B12 or folate can lead to macrocytic anemia. Megaloblastic anemia, a type of macrocytic anemia, is characterized by the production of fewer but larger RBCs called macrocytes, in addition to some cellular changes in the bone marrow. Other laboratory findings associated with megaloblastic anemia include decreased white blood cell (WBC) count and platelet count.

B12 deficiency can lead to varying degrees of neuropathy, nerve damage that can cause tingling and numbness in the affected person's hands and feet. Folate deficiency during early pregnancy can increase the risk of neural tube defects such as spina bifida in a growing fetus. B12 and folate deficiencies are most often caused by insufficient dietary intake, inadequate absorption, or by increased need as seen in pregnancies.

Insufficient intake is uncommon in the United States because many foods and drinks are supplemented with these vitamins, which are stored by the body. Adults typically have several years' worth of vitamin B12 stored in the liver and about 3 months of stored folate. Dietary deficiencies do not usually cause symptoms until the stores have been depleted. B12 deficiencies are sometimes seen in vegans (those who do not consume any animal products) and in their breast-fed infants.

Vitamin B12 absorption occurs in a series of steps. B12 is normally released from food by stomach acid and then, in the small intestine, is bound to intrinsic factor (IF), a protein made by parietal cells in the stomach. This B12-IF complex is then absorbed by the small intestine, bound by carrier proteins (transcobalamins), and enters the circulation. If a disease or condition interferes with any of these steps, then B12 absorption is impaired.

Decreased levels of vitamin B12 and folate due to increased need can be seen with a variety of diseases and conditions. Increased demand for folate occurs during pregnancy, lactation, early childhood, cancers, and chronic hemolytic anemias. All pregnant women need increased amounts of folate for proper fetal development and are encouraged by their physicians to take supplements.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

Fasting for 6-8 hours before sample collection may be required. Ask your health care provider or lab for specific instructions.

The Test

Common Questions

Ask a Laboratory Scientist

Form temporarily unavailable

Due to a dramatic increase in the number of questions submitted to the volunteer laboratory scientists who respond to our users, we have had to limit the number of questions that can be submitted each day. Unfortunately, we have reached that limit today and are unable to accept your inquiry now. We understand that your questions are vital to your health and peace of mind, and recommend instead that you speak with your doctor or another healthcare professional. We apologize for this inconvenience.

This was not an easy step for us to take, as the volunteers on the response team are dedicated to the work they do and are often inspired by the help they can provide. We are actively seeking to expand our capability so that we can again accept and answer all user questions. We will accept and respond to the same limited number of questions tomorrow, but expect to resume the service, 24/7, as soon as possible.

Article Sources

« Return to Related Pages

NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Sources Used for Current Review

(Reviewed 2011 April 4). Vitamin B12. MedlinePlus Drug Information [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/druginfo/natural/926.html through http://www.nlm.nih.gov. Accessed August 2011.

(Reviewed 2011 June 24). Dietary Supplement Fact Sheet: Vitamin B12. NIH Office of Dietary Supplements [On-line information]. Available online at http://ods.od.nih.gov/factsheets/VitaminB12-QuickFacts/ through http://ods.od.nih.gov. Accessed August 2011.

Mayo Clinic Staff (2011 March 4). Vitamin Deficiency Anemia. MayoClinic.com [On-line information]. Available online at http://www.mayoclinic.com/health/vitamin-deficiency-anemia/DS00325/METHOD=print through http://www.mayoclinic.com. Accessed July 2011.

(Revised 2011 April). Pernicious Anemia. National Heart Lung and Blood Institute [On-line information]. Available online at http://www.nhlbi.nih.gov/health/dci/Diseases/prnanmia/prnanmia_what.html through http://www.nhlbi.nih.gov. Accessed August 2011.

Chen, Y. (Updated 2010 January 31). Anemia – B12 deficiency. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000574.htm through http://www.nlm.nih.gov. Accessed August 2011.

Schick, P. (Updated 2011 May 26). Megaloblastic Anemia. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/204066-overview through http://emedicine.medscape.com. Accessed August 2011.

Frank, E. et. al. (Updated 2010 September). Megaloblastic Anemia. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/MegaloblasticAnemia.html through http://www.arupconsult.com. Accessed July 2011.

Conrad, M. (Updated 2011 May 26). Pernicious Anemia. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/204930-overview through http://emedicine.medscape.com. Accessed August 2011.

Dugdale, D. (Updated 2008 November 23). Pernicious anemia. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000569.htm through http://www.nlm.nih.gov. Accessed August 2011.

OH, R. and Brown, D. (2003 March 1). Vitamin B12 Deficiency. Am Fam Physician. 2003 Mar 1;67(5):979-986. [On-line information]. Available online at http://www.aafp.org/afp/2003/0301/p979.html through http://www.aafp.org. Accessed August 2011.

Pagana, K. D. & Pagana, T. J. (© 2011). Mosby’s Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 468-470, 1038-1039.

McPheresen RA, Pincus MR. Henry’s Clinical Diagnosis and Management by Laboratory Methods, 22nd ed. Elsever Saunders: Philadelphia, 2011.

Jacobs DS, DeMott WR, Oxley DK. Jacobs & DeMott Laboratory Test Handbook, 5th ed. LexiComp: Cleveland2001.

Saenger AK. Red cell folate testing: Unwarranted and overutilized in the era of folic acid supplementation. November 2010 . Mayo Medical Laboratories. Available online at http://www.mayomedicallaboratories.com/articles/hottopics/transcripts/2010/2010-11a-rbc/2010-11a-rbc.html through http://www.mayomedicallaboratories.com. Accessed August 2011.

Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Burtis CA, Ashwood ER, Bruns DE, eds. St. Louis: Elsevier Saunders; 2006,  Pp1100-1103.

Kasper DL, Braunwald E, Fauci AS, Hauser SL, Longo DL, Jameson JL eds, (2005). Harrison's Principles of Internal Medicine, 16th Edition, McGraw Hill, Pp 601-604.

Sources Used for Previous Review

Thomas, Clayton L., Editor (1997). Tabers Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Cohen, E. (2003 April 25). Medical Encyclopedia: Folate-deficiency anemia. MEDLINEplus Health Information, Medical Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000551.htm through http://www.nlm.nih.gov/medlineplus/encyclopedia.html.

Brose, M. (2003 June 1). Medical Encyclopedia: Folic acid - test. MEDLINEplus Health Information, Medical Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003686.htm through http://www.nlm.nih.gov/medlineplus/encyclopedia.html.

Angelo, S. (2003 January 19). Medical Encyclopedia: Folic acid (folate). MEDLINEplus Health Information, Medical Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/002408.htm through http://www.nlm.nih.gov/medlineplus/encyclopedia.html.

Angelo, S. (2003 January 18). Medical Encyclopedia: Vitamin B12. MEDLINEplus Health Information, Medical Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/002403.htm through http://www.nlm.nih.gov/medlineplus/encyclopedia.html.

Folate, RBC and Serum. ARUPs Guide to Clinical Laboratory Testing. Available online at http://www.aruplab.com/guides/clt/tests/clt_a237.jsp#1149156 through http://www.aruplab.com.

Intrinsic Factor Blocking Antibody. ARUPs Guide to Clinical Laboratory Testing. Available online at http://www.aruplab.com/guides/clt/tests/clt_a23b.jsp#1152989 through http://www.aruplab.com.

Vitamin B12. ARUPs Guide to Clinical Laboratory Testing. Available online at http://www.aruplab.com/guides/clt/tests/clt_259c.jsp#1150535 through http://www.aruplab.com.

Vitamin B12 Binding Capacity. ARUPs Guide to Clinical Laboratory Testing. Available online at http://www.aruplab.com/guides/clt/tests/clt_260c.jsp#1150556 through http://www.aruplab.com.

Stevenson, R. Spina bifida. AccessMed Health Information Library, Hendrick Health System. Available online at http://www.ehendrick.org/healthy/001280.htm through http://www.ehendrick.org.

Carson-DeWitt, R. Pernicious anemia. AccessMed Health Information Library, Hendrick Health System. Available online at http://www.ehendrick.org/healthy/001049.htm through http://www.ehendrick.org.

Haggerty, M. Folic acid deficiency anemia. AccessMed Health Information Library, Hendrick Health System. Available online at http://www.ehendrick.org/healthy/000554.htm through http://www.ehendrick.org.

Patience Paradox. Folic acid. AccessMed Health Information Library, Hendrick Health System. Available online at http://www.ehendrick.org/healthy/002072.htm through http://www.ehendrick.org.

Haggerty, M. Anemias. AccessMed Health Information Library, Hendrick Health System. Available online at http://www.ehendrick.org/healthy/ through http://www.ehendrick.org.

Vitamin B12. NIH Clinical Center, Facts About Dietary Supplements. Available online at http://www.cc.nih.gov/ccc/supplements/intro.html through http://www.cc.nih.gov.

Folate. NIH Clinical Center, Facts About Dietary Supplements. Available online at http://www.cc.nih.gov/ccc/supplements/intro.html through http://www.cc.nih.gov.

Johnson, L. Vitamin B12. Merck Manual Second Home Edition, Section 12. Disorders of Nutrition and metabolism, Chapter 154. Vitamins. Available online at http://www.merck.com/pubs/mmanual_home2/sec12/ch154/ch154j.htm through http://www.merck.com.

Johnson, L. Folic Acid. Merck Manual Second Home Edition, Section 12. Disorders of Nutrition and metabolism, Chapter 154. Vitamins. Available online at http://www.merck.com/pubs/mmanual_home2/sec12/ch154/ch154k.htm through http://www.merck.com.

(2003 October). Vitamin B-12. familydoctor.org. Available online at http://familydoctor.org/765.xml through http://familydoctor.org/765.xml.

Pagana, Kathleen D. & Pagana, Timothy J. (© 2007). Mosbys Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 460-461, 999-1000, 834-836.

Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry, AACC Press, Washington, DC. Pp 405-406.

Wu, A. (2006). Tietz Clinical Guide to Laboratory Tests, Fourth Edition. Saunders Elsevier, St. Louis, Missouri. 1124-1127, 410-413.

Levin, M. (2007 March 13, Updated). Vitamin B12 level. MedlinePlus Medical Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003705.htm throughhttp://www.nlm.nih.gov/medlineplus/encyclopedia.html. Accessed on 1/30/08.

Matsui, W. (2007 February 14, Updated). Anemia B12 deficiency. MedlinePlus Medical Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000574.htm throughhttp://www.nlm.nih.gov/medlineplus/encyclopedia.html. Accessed on 1/30/08.

Grund, S. (2007 August 27, Updated). Pernicious Anemia. MedlinePlus Medical Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000569.htm throughhttp://www.nlm.nih.gov/medlineplus/encyclopedia.html. Accessed on 1/30/08.

Van Voorhees, B. (2006 October 17, Updated). Folate Deficiency. MedlinePlus Medical Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000354.htm throughhttp://www.nlm.nih.gov/medlineplus/encyclopedia.html. Accessed on 1/30/08.