The effect of sampling procedures on the urate and lactate concentration in oral fluid

The urate concentration in oral fluid decreased with the increase of the stimulation and oral fluid flow rate (r = − 0.98, p = 0.01). Also, the lactate concentration was much (p = 0.03, two tailed) lower in samples collected under a mild stimulation (50 min− 1) than in samples collected without stimulation. Nevertheless, it progressively increased at higher stimulations (100 and 150 min− 1). A transfer process mediated by membrane carriers (i.e. urate transporter and organic anion transporters) was hypothesized to explain these results. Finally, a reduced variability (relative standard deviation below 10%) of the urate concentration was obtained when oral fluid was sampled at constant stimulation (70 min− 1), but it increased remarkably (20-50%) in case of sampling at self-selected pace. Nevertheless, expressing the salivary excretion of urate as a function of time (μg min− 1), the variability of sampling procedure at self-selected pace was lower than 15%.