Abstract
It is the goal of Therapeutic Drug Monitoring (TDM) to use drug concentrations to manage a patient's medication regime and optimise outcome. Limited resources require that drug assays should only be performed when they do contribute to patient management. For this to be the case a therapeutic drug monitoring service has a far greater role than just therapeutic drug measuring. This article describes the roles and functions of a Best Practice TDM service. The features which can and should be strived for in each step of the TDM process-the decision to request a drug level, the biological sample, the request, laboratory measurement, communication of results by the laboratory, clinical interpretation and therapeutic management-are discussed.