Concepts for the rational selection of assays to be used in monitoring therapeutic drugs.

As the domain of monitoring therapeutic drugs rapidly expands from experimental investigations to everyday patient care, all clinical laboratory scientists, but especially clinical chemists, must learn to deal with their involvement in this expansion. First, the theoretical concepts underlying clinical pharmacology must be appreciated so that the laboratory's participation in it can succeed. Individual differences cause unpredictable variations of response to the customarily standardized drug dosage. Properly used, assays of drugs in blood can eliminate such variabilities. Second, the practical selection of which drug assays a laboratory intends to provide must be based on a rational evaluation of assay usefulness, integrating both clinical and laboratory considerations. Such a decision model is suggested; it is generally applicable in allocating priorities among an ever-increasing number of proposed tests under the constraint of finite resources.