Is it possible to pass 3 home drug test kits but fail the lab one?

[Vlad s]

To make a long story short i applied for a few jobs and stayed clean. Two months passed no one called so i figured i didn't get any of them. Sure enough next day i got a call saying i go tone of the jobs and i need to take the urine test next week. So tomorrow will be 7 days since i didn't smoke and have to take the drug test. I exercised a lot these 7 days. Drank Lots of water etc. I bought three home drug tests from three different companies and passed all of them. What is the probability of passing three different drug test kits and failing the lab one. ( BTW its for marijuana).

[cynica]

If they take blood or a hair sample you won't pass it. If it is a urine and you are not a regular smoker then you may just get lucky this time.