Question about some lab results

[TLO]

www.chiefsplanet.com is where I head to get all of my medical questions answered! (Seriously though I know we have some people here knowledgeable about this stuff)

Went in to do my yearly drug screening due to me taking a benzodiazepine on a regular basis about a week ago. Got the results a day later along with a call from my doctor saying that my test came back negative for benzos. They asked me if I had been taking the medication as prescribed, which I have. They said no big deal, we'll just redo the test.

Did the sample again yesterday, and again it was negative. The doctors office isn't open today so I'm not sure what the deal is.

Anyone know why I'd be coming up negative on the screening? Klonipon is the drug, if that helps any.