The need for a sufficient number of low level sera in comparisons of different serum vitamin B12 assays.

Eight radiochemical methods for the assay of vitamin B12 in serum were compared with the microbiological assay with Lactobacillus leichmannii ATCC 7830 using 198 individual sera of patients. There was a good agreement between the results of most samples with some kits and the microbiological assay. However, especially in the sera of vitamin B12-deficient patients large discrepancies between the results could occur.

Formation of HCG in the human fetoplacental unit.

HCG and beta-HCG were determined in umbilical arterial and venous blood immediately after spontaneous term delivery. HCG and beta-HCG are present in higher concentrations in arterial than in venous umbilical cord blood. The data are consistent with the hypothesis that HCG and beta-HCG are produced in the fetal compartment of the human fetoplacental unit, with a larger contribution of the female fetus as compared with the male.