Vitamin B-12 level

Definition:

A test to determine the level of Vitamin B-12 in the blood.

How the test is performed:

Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

How to prepare for the test:

Fast for 6 to 8 hours before the test. Consult with the health care provider if you are using medications that may affect test results, including colchicine, neomycin, para-aminosalicylic acid, and phenytoin.

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:

infant test or procedure preparation (birth to 1 year)
toddler test or procedure preparation (1 to 3 years)
preschooler test or procedure preparation (3 to 6 years)
schoolage test or procedure preparation (6 to 12 years)
adolescent test or procedure preparation (12 to 18 years)

How the test will feel:

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed:

This test is most often performed when other tests (which may include CBC, RBC indices, reticulocyte count, blood smear, or others) indicate the presence of a megaloblastic anemia.

Pernicious anemia is the megaloblastic anemia caused by malabsorption of Vitamin B12. This is usually caused by decreased production of intrinsic factor, a substance essential to Vitamin B12 absorption, in the stomach. This test may also be performed as part of the testing to determine the cause of nervous system disorders.

Normal Values:

200 to 900 pg/ml

Note: pg/ml = picogram per milliliter

What abnormal results mean:

Values of less than 100 pg/ml (picogram per milliliter) indicate a clinically significant deficiency of Vitamin B12 (symptoms are likely to be present or develop).

Causes of deficiency B12 include:

inadequate intake (rare except with strict vegetarian diet)
malabsorption diseases (for example, celiac disease and sprue)
lack of intrinsic factor
hypermetabolic state (for example, with hyperthyroidism)
pregnancy

Increased Vitamin B12 levels are uncommon, because normally excessive B12 is excreted in the urine. However, it may occur with disorders that affect the levels of proteins that bind Vitamin B12 in the serum, including:

hepatic (liver) disease (such as cirrhosis or hepatitis)
myeloproliferative disorders (for example, myelocytic leukemia)

Additional conditions under which the test may be performed:

What the risks are:

Risks associated with venipuncture are slight:

excessive bleeding
fainting or feeling light-headed
hematoma (blood accumulating under the skin)
infection (a slight risk any time the skin is broken)
multiple punctures to locate veins

Special considerations:

In testing for megaloblastic anemias of any sort, serum or red blood cell folate levels are usually also obtained.

Assay for blood levels of Vitamin B12 has become much more accurate within the past few years because of improved testing abilities (a fewer number of false-normal values are obtained, only biologically active B12 is measured).

The cause of a Vitamin B12 deficiency is usually determined by the Schilling test.

Hemolysis of the blood sample (rupture of some of the red blood cells) may affect test results.

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Review Date: 11/26/2001
Reviewed By: Rebecca Elstrom, M.D., Division of Hematology-Oncology, University of Pennsylvania Medical Center, Philadelphia, PA. Review provided by VeriMed Healthcare Network.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org). URAC's accreditation program is the first of its kind, requiring compliance with 53 standards of quality and accountability, verified by independent audit. A.D.A.M. is among the first to achieve this important distinction for online health information and services. A.D.A.M. is also a founding member of Hi-Ethics (www.hiethics.com) and subscribes to the principles of the Health on the Net Foundation (www.hon.ch).

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. Copyright 2003 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.