Evaluation and modification of a radioimmunoassay for pregnancy-specific beta 1-glycoprotein

The radioimmunoassay available from Behringwerke for pregnancy-specific beta 1-glycoprotein (SP 1) was tested for its ability to detect pregnancy prior to the first missed menstrual period. It was found that the equine serum, used as solvent for the standards, did not react like human serum. The standard solvent was replaced by bovine serum albumin 50 g/1 and pooled human serum respectively. Equilibrium and sequential incubation procedures were compared. The latter appeared to be more sensitive in the low value range and was therefore more suitable for the early detection of pregnancy. Also, with standards in albumin, the sequential assay was more specific. SP1 could be detected in sera of men and non-pregnant women, using albumin as standard solvent. This could be due to different cross reacting material of the protein matrix, or to the presence of SP1- like material in human sera. The choice of human male serum seemed to be the most practical. It has also been adopted by Behring, and a commercial kit has been prepared.