Radioimmunoassay of progesterone and estriol in plasma using antibodies immobilized onto protein A-Sepharose CL-4B.

Protein A-Sepharose CL-4B was used as a solid phase for antibodies in the radioimmunoassay of progesterone and estriol. The method was fast and easily standardizable. Immobilized antibodies had the same binding capacity as free antibodies and gave good correlation curves (r = 0.996 for progesterone and r = 0.989 for estriol). Sensitivity was 12.5 pg/tube for progesterone and 8.0 pg/tube for estriol. Comparison of progesterone radioimmunoassay with chemically immobilized antibody onto Sepharose CL-4B was also carried out.