Vitamin B-12 level

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:
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 experience, 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:



How it Feels:
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 .

Risks:
Risks associated with venipuncture are slight:

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



Why this 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 a vitamin B12 deficiency.

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

Abnormal Results:
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:

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:

Additional conditions under which the test may be performed:



Cost:
The estimated cost is $48.

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.