Urine is the most common body fluid chosen for drug testing in clinical toxicology laboratories. It is much less expensive to analyze than blood, hair, sweat, or saliva. Urine is also easily and noninvasively collected. It is also a very clean matrix in comparison to blood, having lower protein concentration, allowing cleaner injections for mass spectrometers. Urine allows for a relatively long window of detection in urine (typically 1 to 3 days).
Forensic drug testing, in which there is a rigorous chain of custody required as the specimen is moved and handled, employs drug testing for the purpose of providing 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 aid emergency room physicians in diagnosis
- To make an initial diagnosis of drug abuse, addiction, or overdose
- To assist in medication adherence
- To monitor compliance in addiction medicine patients
- To monitor compliance within a pain management program
Urine drug testing is ultimately used to improve patient care. Therefore, interpretation of the results is very important. Just like any other diagnostic test, an inappropriate interpretation can adversely affect patient care. The physician should consult with the laboratory director or toxicologist when uncertain of the interpretation of the results of a urine drug test.
