Identifying plasma glycerol concentration associated with urinary glycerol excretion in trained humans.

Glycerol has been used as a means to legitimately hyperhydrate the body in an attempt to offset the deleterious effects of dehydration. It has the potential to mask blood doping practices and as a result has been added to the WADA prohibited substance list. The purpose of this study was to identify the plasma glycerol concentration coinciding with urinary glycerol excretion. Twelve healthy, trained male subjects completed five separate trials under resting conditions. For each trial, subjects consumed a different glycerol dose (0.025, 0.05, 0.10, 0.15, or 0.20 g glycerol/kg LBM) of a 5% glycerol solution in order to determine at what plasma glycerol concentration an increase in urine glycerol concentration becomes apparent. Based on regression analysis, plasma glycerol concentrations > 0.327 ± 0.190 mmol/L and a glycerol dose > 0.032 ± 0.010 g glycerol/kg LBM would be associated with urinary glycerol excretion. There were significant linear relationships between peak plasma glycerol concentration and time to reach peak plasma glycerol concentration to the ingested glycerol doses. Our findings illustrate the importance of considering the effect of urinary glycerol excretion on legitimate hyperhydration regimens as well as suggesting that it is possible to detect surreptitious use of glycerol as a masking agent through urinary analysis.