It would depend entirely on the drs surgery and which supplier they buy from. When I was TTC DD, I had a friend in the medical industry who supplied me with the sort they use at the hospital, they go for a fairly early detection type since it's important to know if a woman with abdominal pain is pg. I imagine the problem with the dr doing a dip test is it's not going to be FMU. Remember tho, HcG levels double every day, so it's possible to get both a false positive or a false negative, best thing is to get a blood test done, that's pretty accurate.
Good luck.