Comparison of different antibody–conjugate derivatives for the development of a sensitive and specific progesterone assay

Antibodies raised against progesterone with hormone-carrier protein bridges placed at four different carbon positions were used to compare the sensitivity and specificity of homologous and heterologous enzyme-hormone conjugates. All heterologous assays were at least twice as sensitive as the corresponding homologous assays. The best results were obtained by using antibodies against 7α-carboxyethyl-thioether-progesterone with 6β-hemisuccinate-progesterone conjugate (or hemimaleate). The sensitivity with human sera was 0.25 ng ml -1 and, the highest crossreaction 10% with 5β-pregnane-3,20-dione, andreproducibility, recovery and accuracy were satisfactory. The correlation coefficient with radioimmunoassay in 103 human sera tested was r=0.915