Test Code: 4018CPT: 82607
|Use||Vitamin B12 deficiency can be used to identify pernicious anemia or is the result of gastrectomy, malabsorption due to surgical resections, and a variety of bacterial or inflammatory diseases affecting the small intestine.|
|Clinical Utility||Vitamin B12 is the name given to any one of a group of substances termed cobalamins. Cobalamins are obtained from animal products such as meat, eggs, milk, and other dairy products. When ingested, they are bound by a protein termed intrinsic factor in the gastric juice of the stomach and are subsequently absorbed in the ileum. Deficiency of this vitamin can lead to megaloblastic anemia and ultimately severe neurological problems. Megaloblastic anemia is characterized by the enlargement and reduction in number of all rapidly proliferating cells of the body, including marrow cells, and is primarily a result of the decreased capacity for DNA synthesis.1,2
Vitamin B12 deficiency can occur for one of several reasons, the most common is a defect in the ecretion of intrinsic factor, resulting in inadequate vitamin B12 absorption from foods, which causes pernicious anemia and is most common in people over age 50.4 Other causes of vitamin B12 deficiency are gastrectomy, malabsorption due to surgical resections, and a variety of bacterial or inflammatory diseases affecting the small intestine. The amount of vitamin B12 absorbed is directly proportional to the length of functional intestine. Vitamin B12 deficiency due to insufficient dietary intake is rare and can occur only after years of abstinence from all animal products.4,5
Elevated levels of vitamin B12 have been associated with pregnancy, the use of oral contraceptives and multivitamins, and in myeloproliferative diseases such as chronic granulocytic leukemia and myelomonocytic leukemia.
Because vitamin B12 and folic acid are linked by the reaction pathway for methionine synthesis, a deficiency in either will disrupt this metabolic pathway and lead to the same symptoms and medical problems. It is usually necessary to measure both vitamins in a clinical workup, with the treatment depending on which of the two is deficient.7
|Intended Patient Population||18+ and Older Adult Males & Females|
|Patient Preparation||Patients should be asked to discontinue use of suplements containing biotin or other B vitamins as these may interfere and result in an abnormally high value.|
|Tube||Red, Green, Tiger|
|Volume||4mL Whole Blood (1mL Serum/Plasma)|
|Min Sample Volume||0.5 mLs|
|Reference Ranges||M & F ≥ 18 yrs old; 180.00-914.00 pg/mL|
|Analytical Measurement Range||50.00-1500.00 pg/mL|
|Test Methodology||Chemiluminescent Immunoassay|
|Test Turnaround Time||2 Days|
|Limitations||Approximately 50% of patients with pernicious anemia have intrinsic factor antibodies.10 The initial denaturation
step in the Vitamin B12 assay inactivates intrinsic factor blocking antibodies. However, in very rare cases,
some samples may not be inactivated due to the heterogeneity or extremely high titer of the intrinsic factor
antibodies.11 Such interfering antibodies may cause erroneous results. Patients should be further evaluated if
suspected of having these antibodies or if the Vitamin B12 results are in conflict with other clinical or laboratory
|Shipping||Refrigerated; Light Sensitive|
|Specimen Stability||7 Days RF|
|Reject Criteria||Hemolysis, Excess Light Exposure|
|Laboratory Developed Test (LDT)||Yes|
|References||1. Shenkin A, Baines M, Fell GS, et al: Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Edited by CA Burtis, ER Ashwood, DE Bruns. St. Louis, Elsevier, Inc, 2006, pp 1100-1105
2. Burtis AC, Ashwood ER, eds. "Vitamin B12. Textbook of Clinical Chemistry. Philadelphia, Pa: WB Sanders Co;1996: 2047-2048.
3. Ryan-Harshman M, Aldoori W. Vitamin B12 and health. Can Fam Physician. 2008 Apr; 54(4):536-541. PubMed 18411381
4. Hvas AM, Nexo E. Diagnosis and treatment of vitamin B12 deficiency—An update. Haematologica. 2006 Nov; 91(11):1506-1512. PubMed 17043022
5. Ryan-Harshman M, Aldoori W. Vitamin B12 and health. Can Fam Physician. 2008 Apr; 54(4):536-541. PubMed 18411381
6. Molloy AM, Kirke PN, Troendle JF, et al. Maternal vitamin B12 status and risk of neural tube defects in a population with high neural tube defect prevalence and no folic acid fortification. Pediatrics. 2009 Marl
7. Steinkamp RC. Vitamin B12 and folic acid: Clinical and pathophysiological considerations. In: Brewster MA, Naito HK, eds. Nutritional Elements and Clinical Biochemistry. New York, NY: Plenum Publishing Corp;1980:169-240.
8. Chanarin I. The megaloblastic anaemias 3rd ed. Blackwell Scientific Publications, Oxford, 1990.
9. Taylor KB. Immune aspects of pernicious anaemia and atrophic gastritis. Clin Haematol 1976; 5: 497-519.