Yes, there were a couple of ladies in our baby buddies thread who still didn't get a +ve with a home test even after the doc had confirmed with a blood test. The blood tests are far more accurate...if there is any doubt you can ask your dr for a quantitative HCG test which tests the actual level in the blood - depending on how many days after conception it should be a certain level which can help to rule out chemical pregnancies, etc.

Good luck!!