[Problems of dextran-charcoal-separation of free from antibody-bound steroid in a direct radioimmunoassay of progesterone without chromatography and extraction (author's transl)].

A method for radioimmunoassay of serum progesterone is described which does not require extraction. A chromatographic step is not necessary because of the high specifity of the antibody. The intrassay coefficient of variation was 6.1% and the interassay coefficient of variation was 8.4%. The detection limit was 10 pg/tube that means 1 ng/ml serum. The test on parallelity was correct up to 10 microliter serum. The results compared with results of a radioimmunoassay with extraction were identical. High concentrations of hormone in serum and an antibody of high specifity are required for the direct radioimmunoassay of steroids. Using the dextran-charcoal system for separation of free from antibody-bound steroid the relationship of the quantity of serum to the quantity of charcoal is of great importance. These problems are discussed.