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Abstract
Many zeranol immunoassay test kits cross-react with toxins formed by naturally occurring Fusarium spp. fungi, leading to false-positive screening results. This paper describes the evaluation and application of recently published, dry reagent time-resolved fluoroimmunoassays (TR-FIA) for zeranol and the toxin α-zearalenol. A ring test of bovine urine fortified with zeranol and/or α-zearalenol in four European Union National Reference Laboratories demonstrated that the TR-FIA tests were accurate and robust. The α-zearalenol TR-FIA satisfactorily quantified α-zearalenol in urine fortified at 10–30 ng ml−1. The specificity-enhanced zeranol TR-FIA accurately quantified zeranol in the range 2–5 ng ml −1 and gave no false-positive results in blank urine, even in the presence of 30 ng ml−1 α-zearalenol. Zeranol TR-FIA specificity was demonstrated further by analysing incurred zeranol-free urine samples containing natural Fusarium spp. toxins. The TR-FIA yielded no false-positive results in the presence of up to 22 ng ml−1 toxins. The performance of four commercially available zeranol immunoassay test kits was more variable. Three kits produced many false-positive results. One kit produced only one potential false-positive using a protocol that was longer than that of the TR-FIA. These TR-FIAs will be valuable tools to develop inspection criteria to distinguish illegal zeranol abuse from contamination arising from in vivo metabolism of Fusarium spp. toxins.
