A number of serious conditions may be associated with an elevated serum vitamin B12 concentration. Some of these conditions may explain why a patient can have a normal or elevated serum vitamin B12 concentration yet evidence of a vitamin B12 deficiency.


Reasons for an elevated serum vitamin B12:

(1) recent administration of vitamin B12 (with or without impaired excretion)

(2) impaired excretion (especially with liver disease)

(3) increased transport proteins (transcobalamin II and haptocorrin)


NOTE: As with hormones the important concentration for vitamin B12 is the amount available to cells for use. Vitamin B12 tightly bound to a transport protein may be measured by a serum assay yet not readily available to cells.


Conditions associated with elevated serum vitamin B12:

(1) chronic renal failure

(2) severe congestive heart failure

(3) diabetes mellitus

(4) increased serum concentration of transcobalamin

(5) increased serum haptocorrin (from myeloid and other cells)

(6) leukocytosis or leukemoid reaction

(7) myeloproliferative disorder

(8) acute or chronic leukemia

(9) acute or chronic liver disease (hepatitis, cirrhosis, cholestasis)

(10) hepatocellular carcinoma or metastases to the liver

(11) disseminated carcinoma

(12) recent infusion of vitamin B12

(13) protein malnutrition

(14) immune complexes between IgG or IgM with vitamin B12


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