Criteria
Serum vitamin B12 levels
The likelihood of vitamin B12 deficiency can be defined according to the serum vitamin B12 level as follows:[1][2]
Probable vitamin B12 deficiency: <200 picograms/mL
Possible vitamin B12 deficiency: 201 to 350 picograms/mL
Unlikely vitamin B12 deficiency: >350 picograms/mL.
Vitamin B12 level >350 picograms/mL does not exclude vitamin B12 deficiency, particularly if pernicious anemia is suspected. Spuriously normal or high serum vitamin B12 levels have been reported in patients with pernicious anemia due to anti-intrinsic factor antibody (anti-IFAB) interference in laboratory assays.[3][4][5][6]
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