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Over the years, falsely normal (or elevated) levels of Serum B12 have
been attributed to liver disease, myeloproliferative disorders, and
antecedent administration of Cyanocobalamin.
In addition, End-Stage Renal Disease patients may have spuriously
elevated Serum B12 levels. This phenomena is two-fold. Impaired
cellular uptake of Vitamin B12 can occur in uremia. Anuric patients, or
those with negligible creatinine clearances, would have diminished (or a
complete lack of) urinary vitamin excretion.
Another scenario receives much less attention. When testing Serum
B12 in patients who have received long-term B12 antagonists (such as
Colchicine), it is imperative that Serum B12 testing be contemporaneous
with the use of the B12 antagonist. If Colchicine were to be discontinued
in advance of Serum B12 testing, the result could no longer be relied upon
to accurately assess intracellular vitamin levels. In fact, those levels
should be assumed to be falsely elevated. Colchicine-induced
malabsorption has been shown to revert to normal absorption within 2-5
days (upon cessation of the drug). This reflects the accelerated mitotic
rate of intestinal villi.