Synonym

• Antipernicious anemia factor assay
• B12 (Vitamin) level
• Cyanocobalamin levels
• Extrinsic factor
• VB₁₂ levels

Tubes

• Red or tiger top tube
• 5 mL of venous blood

Additional information

• Fasting for 6-8 hrs before test
• Protect the sample from light
• Handle sample gently to prevent hemolysis
• Send sample to lab immediately
• If delayed separate and freeze serum
• Avoid exposure to radioisotopes, therapeutically or diagnostically (Schilling test), prior to the test
• Draw specimen before vitamin B₁₂ therapy or blood transfusions

Info

• The vitamin B₁₂ assay measures the amount of vitamin B₁₂ in the blood
• Vitamin B₁₂ is a water soluble vitamin containing cobalt, essential for the hematopoiesis, deoxyribonucleic acid (DNA) synthesis and growth, myelin synthesis, CNS integrity, and as a coenzyme to biochemical processes
• Vitamin B₁₂ is derived solely from dietary intake, mainly from animal products such as meat, shellfish, milk, and eggs. It is absorbed in the intestinal mucosa in the presence of an intrinsic factor
• Vitamin B₁₂ is bound to proteins in the serum; 70% to transcobalamin I (TC I) and 30% to transcobalamin II (TC II), which is the physiologically active form

Clinical

• The clinical utility of vitamin B12 assay includes:
• Evaluation of megaloblastic or macrocytic anemia to distinguish it from other forms (such as folate deficiency, alcoholism, etc)
• Evaluation of central nervous system disorders, such as peripheral neuropathy, demyelination
• Aids in the differential diagnosis of anemia and conditions marked by high turnover of myeloid cells, as in the leukemias
• Evaluation in malabsorption syndromes, vegetarians, growth impairment in children, and alcohol abuse
• Evaluation in elderly persons presenting with irritability, confusion, depression, paranoia, and dementia
• Evaluation for vitamin B₁₂ deficiency in patients with gastrointestinal disease, glossitis, abnormalities of taste, previous surgery or radiotherapy to stomach or small bowel
• Evaluation of autoimmune disease of thyroid, parathyroid or adrenals
• Evaluation for vitamin B₁₂ deficiency in persons with family history of pernicious anemia
• Vitamin B12 deficiency is associated with the following manifestations, which include:
• Hematological, such as megaloblastic or macrocytic anemia
• Neurological, such as paresthesias, peripheral neuropathy, and demyelination of the corticospinal tract and dorsal columns
• Psychiatric manifestations including cognitive impairment, psychosis, and dementia
• Cardiovascular such as hyperhomocysteinemia in turn resulting in increased risk of myocardial infarction and stroke
• Vitamin B12 deficiency may be clinically seen as:
• Generalized symptoms and symptoms of anemia
• Anorexia
• Weakness and tiredness
• Fatigue
• Diarrhea
• Numbness and tingling of hands and feet
• Pale skin
• Shortness of breath
• Palpitations
• Sore mouth and tongue (atrophic glossitis)
• Neuropsychiatric manifestations
• Irritability
• Leg stiffness
• Ataxia
• Paresthesia
• Decreased proprioception
• Decreased vibration and position sense
• Hyporeflexia (decreased ankle jerk)
• Memory impairment
• Personality changes
• Depression
• Dementia
• Psychosis
• Optic neuritis
• Excess intake of Vitamin B₁₂ in treatment of megaloblstic anemia can result in hypokalemia due to increased RBC requirements of K⁺ with conversion of megaloblastic to normal erythropoiesis

Additional information

• Vitamin B₁₂ levels are highest in Blacks, intermediate in Hispanics, and lowest in Whites
• Values decrease with age in men
• The measurement of unsaturated Vitamin B₁₂-binding capacity (UBBC) is valuable in distinguishing between untreated polycythemia vera and other conditions in which there is an elevated hematocrit values
• Low Vitamin B₁₂ levels require treatment, intermediate low levels should be followed with serum methylmalonic acid (MMA) test, and borderline low values should be evaluated with other tests
• Vitamin B₁₂ assay is typically performed in conjugation with folate levels. Folate levels can be high in Vitamin B₁₂ deficient individuals
• Current assays measure only active Vitamin B₁₂ and do not cross-react with inactive analogs. The microbial assays are more accurate than radio-immunoassays
• Factors interfering with test results include:
• Hemolysis or exposure of the specimen to light invalidates results
• Failure to follow dietary restrictions
• Blood transfusion within 3 months prior to the specimen collection
• Recent intake of vitamin A and C (false increase)
• Administration of substances that decrease Vitamin B₁₂ absorption
• Smoking
• Pregnancy, large doses of Vitamin C, and folate deficiency may result in a falsely reduced Vitamin B₁₂ microbial assay
• Related laboratory tests include
• Bone marrow biopsy
• Complete blood count
• Endoscopy with duodenal biopsy
• Folate levels
• Homocysteine levels
• Intrinsic factor antibodies
• Pentagastrin-resistant achlorhydria
• Peripheral blood smear for RBC morphology and presence of hypersegmented neutrophils
• RBC indices for mean corpuscular volume (MCV)
• Schilling test
• Serum gastrin levels
• Serum methylmalonic acid (MMA)
• Serum pepsinogen I levels

Nl Result

Consult your laboratory for their normal ranges as these may vary somewhat from the ones listed below.

High Result

Conditions associated with elevated Vitamin B₁₂ levels (>700 pg/mL or >517 pmol/L) include:

• Chronic obstructive pulmonary disease (COPD)
• Chronic renal failure
• Congestive heart failure
• Diabetes
• Excessive dietary intake
• Liver diseas
• Acute or chronic hepatitis
• Cirrhosis
• Liver metastasis
• Myeloproliferative diseases
• Acute and chronic granulocytic leukemia
• Myelomonocytic leukemia
• Leukocytosis (leukemoid reaction)
• Obesity
• Polycythemia vera
• Protein malnutrition
• Uremia
• Drug
• Chloral hydrate
• Omeprazole
• Oral contraceptives
• Valproic acid

Low Result

Conditions associated with decreased Vitamin B₁₂ levels (<100 pg/mL or <74 pmol/L) include:

• Inadequate vitamin B12 intake
• Alcohol abuse
• Elderly persons
• Strict vegetarianism
• Inadequate absorptio
• Deficient or defective intrinsic factor
• Gastric carcinoma
• Gastritis
• Pernicious anemia (megaloblastic anemia)
• Malabsorption syndromes
• Blind loop syndrome with abnormal gut flora
• Celiac disease
• Crohn's disease
• Fistulas
• Ileal resection or bypass
• Regional enteritis
• Total gastrectomy
• Tropical sprue
• Zollinger-Ellison syndrome
• Pancreatic insufficiency
• Chronic pancreatitis
• Cystic fibrosis
• Interference with vitamin B12 absorption
• Bacterial overgrowth
• Drugs (see below)
• Fish tapeworm (Diphyllobothrium latum)
• Rare congenital disorders
• Defective intrinsic factor production
• Orotic aciduria
• Transcobalamin II deficiency
• Others
• Alzheimer disease
• Chronic high-flux hemodialysis
• Dietary folic acid deficiency (rare)
• HIV infection (with or without malabsorption)
• Hyperthyroidism
• Multiple myeloma
• Pregnancy
• Drugs
• Aminosalicylic acid
• Anticonvulsants
• Ascorbic acid
• Aspirin
• Carbamazepine
• Chlorpromazine
• Cholestyramine
• Cimetidine
• Colchicine
• Metformin
• Neomycin
• Nitroprusside
• Octreotide
• Ranitidine
• Rifampin
• Triamterene

References

• Ambroszkiew J et al. Serum homocysteine, folate, vitamin B12 and total antioxidant status in vegetarian children. Adv Med Sci. 2006;51:265-8.
• ARUP's Laboratories®. Vitamin B₁₂. [Homepage on the Internet] ©2007. Last accessed on March 29, 2007. Available at URL: http://www.aruplab.com/guides/ug/tests/0070150.jsp
• eMedicine from WebMD®. Vitamin B-12 Associated Neurological Diseases. [Homepage on the Internet] ©1996-2006. Last updated on July 18, 2006. Last accessed on March 29, 2007. Available at URL: http://www.emedicine.com/neuro/topic439.htm
• Goebels, N et al. Dementia Associated With Vitamin B₁₂ Deficiency. J Neuropsychiatry Clin Neurosci August 2000. 12:389-394.
• Kumar V. Pernicious anemia. MLO Med Lab Obs. 2007 Feb;39(2):28, 30-1.
• LabTestsOnline®. Vitamin B12 & Folate. [Homepage on the Internet]© 2001-2007. Last reviewed on December 22, 2004. Last accessed on March 29, 2007. Available at URL: http://www.labtestsonline.org/understanding/analytes/vitamin_b12/glance.html
• Lechner K et al. [Vitamin B12 deficiency. New data on an old theme]. German. Wien Klin Wochenschr. 2005 Sep;117(17):579-91. Review
• Oh RC et al. Vitamin B12 deficiency. Am Fam Physician. 2003 Mar 1;67(5):979-86. Available at URL: http://www.aafp.org/afp/20030301/979.html
• Reynolds E et al. Vitamin B12, folic acid, and the nervous system. Lancet Neurol. 2006 Nov;5(11):949-60. Review.