My best friend got a BFN on HPT and urine test at docs office, but her bw came back POS and now she has a 3 yr old son. Hope that gives you some hope!
I realy don't know what kind they gave me, but after my IVF I went and got a blood test done and it was NEG. I even had a normal period after that. It has been 2 weeks and today I got a POS on my home test. I am now waiting for my blood test to come back. I don't know how it happened, but it did.
Sounds like you got a qualitative test, which basically only gives you a positive when the levels are over a certain amount (as opposed to the quantitative, which gives you an actual number). But, hey, you never know. I think HCG shows up faster in the blood steam than in urine, so even if your urine test at the doctor's was negative, there might have been more HCG in your blood at the time.
I'm kinda surprised, though, that they didn't give you a quantitative test...but keep your head up! You might get a nice surprise when they call you with the results!
Fingers crossed!!!