Vitamin B12 Deficiency Cascade
Also known as: Megaloblastic Anemia Cascade, Pernicious Anemia Cascade
Use
Diagnosis of Vitamin B12 Deficiency. Although often used as the first-line screening test for B12 deficiency, serum B12 measurement used in isolation has a generally poor sensitivity and specificity for detection of B12 deficiency.1,6,19,32 The National Health and Nutrition Examination Survey (NHANES) opted to use the combination of serum total vitamin B12 and methylmalonic acid (MMA) to monitor B12 status in the United States population.35 In the interest of economy, a number of groups have suggested the use of a sequential selection algorithm for the detection of B12 deficiency.5,14,33,34 In this approach, a second-line assay (in this case MMA) is performed only when the outcome of the first-line assay (vitamin B12 level) falls in an "equivocal" range.1,7 It has been suggested that borderline B12 levels (200-400 ng/L) should be followed up with measuring MMA levels.1 MMA levels below the upper limit of the reference interval (0-378 nmol/L) are strongly suggestive of normal B12 status.
Special Instructions
Patients are advised to stop biotin consumption at least 72 hours prior to sample collection due to potential interference with test results.
Limitations
Ninety percent of patients with pernicious anemia have gastric parietal cell antibodies, but the specificity is low as these antibodies are found in 15% of elderly individuals. If Intrinsic Factor Antibody (IFA) results are negative but pernicious anemia is suspected, elevated serum gastrin might indicate the condition. Mutations in the intrinsic factor gene could also lead to inherited B12 malabsorption similar to pernicious anemia. Discordance between lab results and clinical signs of B12 deficiency should prompt treatment to prevent neurological damage. MMA levels between 300-700 nmol/L in renal failure patients may not respond to B12 administration.
Methodology
Immunoassay
Biomarkers
LOINC Codes
- 2132-9
- 2132-9
- 31443-5
- 8087-9
- 13964-2
Result Turnaround Time
1-2 days
Related Documents
For more information, please review the documents below
Specimen
Serum
Volume
3 mL
Minimum Volume
2 mL
Container
Red-top tube or gel-barrier tube
Collection Instructions
If a red-top tube is used, transfer separated serum to a plastic transport tube.
Patient Preparation
Patients should stop biotin consumption at least 72 hours prior to sample collection.
Storage Instructions
Store specimen at room temperature
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 7 days |
| Refrigerated | 7 days |
| Frozen | 14 days |