Oestrogen radioreceptor assay for multi‐residue screening of bovine urine for oestrogenic anabolic compounds

An improved radioreceptor assay (RRA), based on the method originally described by Korenman (1968), was used for the screening of urine samples of cattle for the presence of exogenous oestrogenic anabolic compounds, i.e. stilbenes and zeranol. The method includes extraction of the hormones from urine samples with a simultaneous purification using reversed-phase C18 cartridges. HPLC is used to isolate the anabolics from the naturally occurring oestrogens. Fractions containing the stilbenes and zeranol are collected and subsequently quantified using the RRA with the oestrogen receptor, isolated from immature calf uteri, as binder and tritiated 17 beta-oestradiol as tracer. Urine samples from untreated calves and cows, as well as samples from calves treated with zeranol/trenbolon acetate, dienoestrol or hexoestrol or samples containing diethylstilboestrol, were analysed using this RRA method. Sensitivity, specificity and predictive values were calculated at different classification levels (0.4, 0.5, 0.6 and 1.0 ng 'apparent' oestradiol per ml urine). An optimum sensitivity (89%) with a maximum specificity (95%) was reached at a classification level of 0.6 ng/ml. At this level the detection limits in urine samples are 0.5 ng/ml for hexoestrol, 0.6 ng/ml for diethylstilboestrol, 0.9 ng/ml for dienoestrol and 5.0 ng/ml for zeranol.