Recognition of deficiency of vitamin B12 using measurement of serum concentration

Of 504 patients with low concentrations of vitamin B12 in serum by microbiologic assay (less than 120 pg/ml) in whom clinical information was available to evaluate vitamin B12 status, 109 (22%) were found to have clinically important deficiency of vitamin B12, and another 10 had pernicious anemia with deficient serum levels of both vitamin B12 and folate. Serum from patients deficient in vitamin B12 was assayed by several commercially available assay techniques. These used either purified or impure preparations of gastric intrinsic factor as binder, extracted cobalamins with either heat or alkali ("no boil") and separated bound from free vitamin B12 either with activated charcoal or by binding the intrinsic factor to glass beads ("solid state"). These kits were purchased commercially from Becton-Dickinson Co. (SimulTrac), BioRad Corp. (Quantaphase), Amersham Corp. (Vitamin B12/folate radioassay) and Corning Medical and Scientific (Immophase). Serum vitamin B12 concentrations assayed in sera from patients deficient in vitamin B12 overlapped the normal range in 6% of all samples assayed by techniques using purified intrinsic factor assays (BioRad, Amersham, and the "blocked" SimulTrac assay), but no such overlap was found between deficient and nondeficient sera assayed with the solid-state pure intrinsic factor assay (Corning), the "unblocked" SimulTrac, or Euglena gracilis. It would appear that (1) radiodilution assays extracting serum by boiling and binding vitamin to binder fixed on a solid matrix may be the most reliable available at this time. These may be as reliable as microbiologic assay for separation of patients with deficiency from those without deficiency.(ABSTRACT TRUNCATED AT 250 WORDS)