Generic immunoassay of corticosteroids with minimum pre-treatment of urine samples

Abstract

A generic, rapid and sensitive enzyme linked immunosorbent assay (ELISA) test has been developed which allows large-scale simultaneous testing of synthetic corticosteroids viz., flumethasone, dexamethasone and betamethasone. This assay can be directly applied to diluted urine samples (1 + 9) without hydrolysis of glucuronide or sulfate conjugates or any other treatment of samples. The polyclonal antibody was obtained by immunizing sheep with a flumethasone derivative linked to human serum albumin. This polyclonal antibody displayed high-reactivity with several synthetic corticosteroids whilst endogenous corticosteroids such as cortisol gave very low cross-reactivity (<0.5%). Sensitivities obtained in this assay were 2.5, 3.1 and 12.5 ng ml^–1 for flumethasone, dexamethasone and betamethasone, respectively. The ability of this assay to detect several synthetic corticosteroids was demonstrated by testing urine samples from horses to which the drugs had been administered.