Cortisol concentrations in post competition horse urine: a French and British survey

The purpose of the present report was to estimate the population parameters of cortisol concentrations in urine, an endogenous hormone used as a 'doping' agent and for which an international threshold (1.0 micrograms/ml) has been proposed. Two data bases (French and UK) corresponding to 112 and 142 samples, respectively were considered. Urine was collected under specific post competition conditions. Cortisol concentrations were obtained by validated methods (HPLC for the French samples, and GC-MS for UK samples). No difference was observed between the 2 data sets and statistical analyses were carried out on the two merged files. The overall geometric mean cortisol concentration was 48 ng/ml. Distribution was not Gaussian. A log-normal distribution was not rejected (for P > 0.05). Using the log-normal distribution, it was calculated that the probability of exceeding a cortisol concentration in urine of 1.0 micrograms/ml was 1.1 x 10(-4). It was concluded that the actual international threshold is specific i.e. robust with regard to the risk of erroneously declaring an unmedicated horse as positive.