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.