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What Affects the Test

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

  • Taking certain medicines that might affect your test results. Tell your doctor all of the medicines that you take.
  • Being pregnant or breast-feeding.
  • Taking large doses of vitamin C.
  • Drinking large amounts of alcohol.
  • Having a test, such as a computed tomography (CT) scan, that used dyes in the past 7 days.
  • Having pernicious anemia, which means you lack the substance (intrinsic factor) needed to absorb vitamin B12.

What To Think About

  • Folic acid levels can be high in people who lack vitamin B12. A folic acid test is often done at the same time as a vitamin B12 test. To learn more, see the topic Folic Acid Test.
  • Methylmalonic acid is a substance in the blood that increases when vitamin B12 levels decrease. A methylmalonic acid (MMA) blood test may be done to help evaluate vitamin B12 test results.
  • A change in homocysteine levels may also affect a change in vitamin B12 levels because of metabolism changes. To learn more, see the topic Homocysteine.

Citations

  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.

ByHealthwise Staff
Primary Medical ReviewerE. Gregory Thompson, MD - Internal Medicine
Specialist Medical ReviewerJoseph O'Donnell, MD - Hematology, Oncology

Current as ofMarch 12, 2014

WebMD Medical Reference from Healthwise

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