Experience with a commercial kit for the radioisotopic assay of vitamin B₁₂in serum: the Phadebas B₁₂Test

Abstract

sYNoPsis The first commercial kit for the radioisotopic assay of vitamin B12 in serum-the Phadebas B12 Test produced higher values than the radioisotopic method of Raven, Robson, Walker, and Barkham (1969) and the Lactobacillus leichmannii microbiological assay. Its normal range was 300-1100 pg/ml and its reproducibility was similar to that of the other radioisotopic method. It should be possible to lower the results obtained by the Phadebas method by modifying its standard curve and to reduce the time taken for the assay by shortening its incubation period.

Extraction of serum vitamin B12 for radio-isotopic and Lactobacillus leichmannii assay.

“…In the radio-isotopic method of Raven et al (1969), some defect in the acid extraction process, the binding of vitamin B12 by intrinsic factor, the separation of free and bound B12 by albumen-coated charcoal or in the calculation of results by equation could lead to consistently high serum vitamin B12 values but it would be difficult to explain why some folate deficient or postgastrectomy sera should give especially discrepant results and why accurate values should be given for vitamin B12 solutions and dilutions of sera. It has already been shown that the calculation of results by equation gives similar results in the 0-1000 pg/ml range to those obtained from a standard curve (Raven et al, 1968) and, in addition, other quite different radio-isotopic assays have produced higher serum vitamin B12 values than the L. leichmannii assay (Raven and Robson, 1974;van de Wiel et al, 1974). The acid extraction process, used in the method of Raven et al (1969) and suggested by Rothenberg (1968) as a cause of falsely high serum vitamin B12 values, will be discussed later.…”

“…In general, those radio-isotopic assays which use an acid extraction process, either hydrochloric or glutamic acid, produce higher serum vitamin B12 values than the L. leichmannii method (Raven et al, 1969;van de Wiel et al, 1974;Raven and Robson, 1974). Those radio-isotopic assays which use a deproteination extraction process produce values in agreement with the L. keichmannii method (Matthews et al, 1967;Britt et al, 1969;Wagstaffand Broughton, 1971).…”

Interlaboratory comparison of serum vitamin B12 assay.

“…biological assay The problem of the RID assay kits is more complicated. Some RID methods have been reported to give higher results than RID charcoal methods (Raven and Robson, 1974). These higher levels were reported with assays using either R-binder (Green et al, 1974) or intrinsic factor (Wide and Killander, 1971;Raven et al, 1969;Raven et al, 1972;Cooper and Whitehead, 1978).…”