Oral fluid as a diagnostic tool.

Technological advances over the past decades have enabled oral fluid to expand its usefulness in the diagnosis of disease, prediction of disease progression, monitoring of therapeutic drug levels and detection of illicit drugs. The easy non-invasive nature of collection and the relationship between oral fluid and plasma levels make oral fluid a valuable clinical tool. This review describes advances over the past 5 years in the area of oral fluid as a diagnostic tool, its use in therapeutic and illicit drug monitoring, including proposed guidelines for cut-off values, and methods of collection.