Question about testing

I had blood and urine taken today at the doctors office for a drug test to be sent to the lab. I was curious how it would turn out so I did a check first home test and it said I was negative for THC. If I passed that then is there a possibilty I could still fail the lab test? It was been a little while since I smoked but not that long(like two weeks or so) but I run or mountain bike almost everyday, drink hardly anything but water, and have very little body fat.

Thanks,
Rm25