Final answer:
Two urine specimens are required for drug testing to guarantee accuracy, reliability, and quality control, with the second specimen offering a means of confirmation or contestation of results.
Step-by-step explanation:
When undergoing drug testing, using two urine specimens, typically labeled as Bottle "A" and Bottle "B," is a standard procedure to ensure the accuracy and reliability of the test results. The first bottle, "A," is used for the initial screening test, while the second bottle, "B," is saved for a confirmation test if the first test indicates a positive result for drug usage. This two-part system addresses potential errors and provides a safeguard against false-positive results. Furthermore, the "B" specimen can be important in cases where the result is contested. It serves as a quality control measure, allowing another accredited laboratory to verify the findings if necessary. Also, intricate sample preparation protocols are often required to ensure the presence and concentration of substances can be observed without interference from other biological compounds.