Quality control in therapeutic drug monitoring.

Quality control of routine drug assays, like most immunoassays, should mainly be the responsibility of each individual laboratory: intra-laboratory quality control. External quality assessment should direct its efforts in particular to non-routine methods and to new assays. However, it may sometimes also be very useful to have laboratory results of routine assays studied in external programmes, since vague requests or difficult interpretations of drug concentrations need discussion outside the individual laboratory.