Abstract
The ultimate purpose of this series of studies is to simplify the technical procedure in the radioassay of vitamin B_12,and the current investigation concerns itself with the use of intrinsic factor (IF) coupled covalently to cyanogen bromide activated cross-linked dextran according to the method of Wide and Killander. The results obtained have been as follow : The Sephadex-IF complex prepared in this way is stable, and the time required for the separation of the bound from the free vitamin B_12 is relatively short. The assay comprises fewer steps. The whole assay can be performed in the same tube. The standard curve may be linearized by applying a logit transformation of the response variables. The method is found to be sensitive, accurate and reproducible. Thus, sera with low vitamin B_12 levels can be measured with accuracy. On the other hand, sera with vitamin B_12 levels over 1,600 pg/ml have to be diluted, because of the range of linearity of the standard curve. The incubation step requires 3 hours and it is somewhat time consuming. In a final step, the precipitating complexes have to be washed, and some loss of Sephadex-IF complexes may occur during the process of withdrawing the supernatant. Some of the potential problems and pitfalls in this type of radio-B_12 solvent assay have been discussed. Nonetheless, this method is suitable for a routine diagnostic test and can be set up in almost any laboratory since the materials are easily avalaible.
