Ditto night_shade:

If it's an employment screen. The panel would identify the presence of opiods, and then processed with a MSGC test which usually confirms the presence of the drugs to avoid a lab error. If you have a script, you have nothing to worry about.

If it's a medical test by a Dr. (ie Bupe Dr. or you are a new patient) it is possible to measure levels as they decrease over time and represent valuable information that Dr.'s need to determine if 1) the patient is being honest
2) potential abuse.

Hopefully your screen is for employment, and you only have the hydro present. Many debates about privacy and employee/employer relationships, but you will be fine if it is a pre-employment screen and you let them know up front about your prescription. I have several friends who have got new jobs in this situation.