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Clinical Significance of Serum Vitamin B₁₂ Measured by Radioassay Using Pure Intrinsic Factor

Eugene L. Saenger Radioisotope Laboratory, University of Cincinnati College of Medicine, Cincinnati, Ohio

Correspondence: For reprints contact: I. W. Chen, Radiobiology Laboratory J-K Annex, Cincinnati General Hospital, Cincinnati, OH 45267.

ABSTRACT

Serum vitamin B₁₂ (B₁₂) levels of 53 patients (15 with pernicious anemia) and 42 healthy volunteers were determined using crude intrinsic factor (IF), pure IF, and a mixture of crude IF + R-protein blocking agent (block IF). The radioassay using pure IF showed less sample-to-sample variation in nonspecific binding than the radioassay using block IF. The mean B₁₂ levels in 42 healthy subjects were significantly higher with crude IF (499 ± 23 pg/ml,1 s.e.m.) than with pure IF (408 ± 29 pg/ml) or with block IF (407 ± 22 pg/ml). B₁₂ levels were abnormally low in all 15 patients with pernicious anemia by pure IF (<100 pg/ml), in 14 patients by block IF (<150 pg/ml), and in only seven patients by crude IF (<200 pg/ml). Our data confirm previous reports that B₁₂ deficiency can be diagnosed more reliably by measuring serum B₁₂ levels with either pure IF or block IF.