Urine is the most common body fluid used for drug testing in clinical toxicology laboratories. Urine is easily and non-invasively collected. It is a very clean matrix compared to blood, with lower protein concentration, allowing for cleaner injections for mass spectrometers. Urine provides a relatively long window of detection in urine, typically 1 to 3 days. Unlike blood, which is quickly cleared of drugs, urine concentrates drugs and their metabolites. This means urine is not only the most convenient sample, but it is also the sample with greater sensitivity due to higher concentrations of analytes.
Forensic drug testing, in which a rigorous chain of custody is required as the specimen is moved and handled, is used to provide evidence in a criminal court. Clinical drug testing, on the other hand, is used in a therapeutic setting for diagnosis and treatment. Both forensic testing and clinical testing employ the same testing methodologies.
There are many reasons why a physician would order a urine drug test:
- To help diagnose an overdose
- To assess if drugs are contributing to observed symptoms in a patient
- To make an initial diagnosis of drug abuse or addiction
- To monitor medication compliance in patients
- To document compliance within a pain management program
Urine drug testing is ultimately used to improve patient care. Therefore, interpretation of the results is critical. An incorrect interpretation can adversely affect patient care, just like any other diagnostic test. The physician should consult with the laboratory director or toxicologist when uncertain of the interpretation of urine drug test results.
