Effect of sampling procedures for the chemical characterization of oral fluid in clinical applications

The possibility to obtain complementary clinical information compared to those gathered from blood and urine in a non-invasive way represents one of the most important and current target in clinical practice, concerning the diagnosis of diseases and monitoring of therapies. The use of oral fluid in the clinical environment is an attractive approach because this technique is less invasive and safe. The non-invasive sampling that does not require trained personnel is the main advantage of oral fluid analysis compared to the analysis of blood and its derivatives (e.g. plasma), thus oral fluid analysis has become popular for human biomonitoring, especially for the screening of large population. There are several methods for collecting non-stimulated (draining, spitting, suction and adsorption into swab) and stimulated (with chemical or masticatory stimulus) oral fluid samples. In this latter approach, oral fluid secretion can be stimulated by applying a few drops of citric acid directly onto the tongue or chewing paraffin wax. After stimulation, sample can be spat out, suctioned or absorbed. Although such fluid is easy to collect, particular attention must be paid to the effect of sampling conditions on the quality of analytical information. For instance, oral fluid concentrations of basic and acidic drugs are largely dependent on variations of the oral fluid pH. In the same way, for hydrophilic drugs, different flow rates obtained with different sampling methods may influence the measured drug concentrations in such fluid, as a more effective stimulation leads to a larger dilution of the sample. In this presentation, the effects of sampling parameters on the chemical composition of oral fluid samples will be discussed and suggestions for the collection of this specimen will be presented.