Help with hydrocodone urine levels. I take 10/325 norco for back pain, when not!

Help with hydrocodone urine levels. I take 10/325 norco for back pain, when not at work.?

I understand the half-life of the drug, as it pertains to blood serum levels. My concern is random urine drug testing at work, where the detection level is 2000ng/ml. If anyone knows a calculation to determine what the level would be, say after 12 hrs of ingestion, your help would be greatly appreciated.

I do have a prescription, which I know will clear my name, I just would like to know if and when I will have to do so.

Thank you so much for your help!

Have your prescription ready.