Therapeutic drug monitoring (TDM) is a branch of clinical chemistry that specializes in the measurement of medication levels in serum. TDM requires that the laboratory make quantitative measurements of drugs and/or their metabolites. These measurements are almost always made on patient serum samples. TDM can be contrasted with urine drug testing. Urine drug testing is usually performed to detect or monitor drug abuse or check patient compliance when a drug with high abuse potential has been prescribed. Determining actual concentrations are less important for urine drugs of abuse screening. Providing accurate concentrations for TDM, on the other hand, is essential. Serum concentrations provided with TDM allow clinicians to adjust medication dosages as well as assess a patient's drug metabolism response and their compliance or dosing regimen.