A urine drug screen is designed to detect illegal (and some prescription) drugs in the urine. See toxicology screen for information about specific drugs.
Drug screen - urine
It is necessary to collect a "clean-catch" (midstream) urine sample. To obtain a clean-catch sample, men or boys should wipe clean the head of the penis with a moist cloth or alcohol square. Women or girls need to wash the area between the lips of the vagina with soapy water and rinse well.
As you start to urinate, allow a small amount to fall into the toilet bowl (this clears the urethra of contaminants). Then, in a clean container, catch about 1 - 2 ounces of urine and remove the container from the urine stream. Give the container to the health care provider or assistant.
You may be asked to remove all your personal belongings and wear a hospital gown. You will then be placed in a room where you have no access to your personal items or water. In this environment, you cannot dilute the sample, nor can you use someone else's urine for the test.
The sample is then taken to the laboratory for evaluation.
The test involves only normal urination.
The test is performed to detect the presence of illegal (and some prescription) drugs in your urine, which indicates recent use of the drugs.
No drugs in the urine.
If the test result is positive, it is helpful to confirm it with gas-chromatography mass spectrometry (GC-MS). In some cases, a test will register a false positive. This can result from interfering factors such as some foods, prescription medications, and other drugs.
The GC-MS will help tell the difference between a false positive or a true positive, resulting from the presence of an illegal drug.
McPherson RA, Pincus MR. Toxicology and therapeutic drug monitoring. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. Philadelphia, Pa: Saunders Elsevier; 2006:chap 23.