Less-invasive measurement of tissue availability of hormones and drugs: diffusion-sink sampling

The use of small diffusion-sink sampling devices allows the relatively noninvasive and unobtrusive collection of a specimen that represents, in a precisely interpretable way, the average freely diffusing concentration of an analyte over a biologically relevant period of time. In an orally worn configuration, these sampling devices reject artifacts arising from blood plasma contamination of saliva and provide a time-averaged sample without requiring the subject to adhere to a frequent-sampling schedule. The practical advantages of noninvasiveness are thus combined with a fairly direct method for measuring what seems, in light of our current understanding, most important to know about the relative abundance of the steroid hormones. Whether this specificity of measurement also has practical benefits has yet to be tested.