An improved radioimmunoassay for the anabolic agent hexoestrol, using a monoclonal antibody.

A monoclonal antibody was raised against hexoestrol coupled to bovine serum albumin. The antibody cross-reacted with the stilbenes, diethylstilboestrol (10%) and dienoestrol (4%), but had no cross-reaction (less than 0.01%) with other anabolic agents. A radioimmunoassay method using the monoclonal antibody has been validated and used to measure residues of hexoestrol in the urine of treated cattle. The limit of detection was 0.6 pg/ml urine at the 95% confidence limit. The results were compared with those obtained using polyclonal antibodies. Although there was a good correlation between the results, the use of monoclonal antibody gave more reliable results than those obtained with available polyclonal antibodies. The monoclonal antibody, because of its quality and theoretically limitless supply, is very suitable for use in large scale screening or monitoring programmes for regulating the use of hexoestrol.