Brief Report: Hemoglobin-Coated Charcoal Radioassay for Serum Vitamin B₁₂. A Simple Modification To Improve Intrinsic Factor Reliability

Reliable binding of vitamin B₁₂ by intrinsic factor (IF) is essential in the hemoglobin-coated charcoal radioassay for serum vitamin B₁₂ as described by Lau et al.⁴ The fact that some IF preparations bind less B₁₂ in the saline IF control tube than in those tubes containing serum can result in a falsely low measurement of unknown sera. This may be avoided by the simple substitution of 0.5 ml. of 5 per cent human albumin solution for the saline in the IF control tube.