Hi Pigletpoo, I've been reading loads of scientific papers of implantation and pregnancy tests in the past few days (I know, sad isn't it!!). It seems that in humans, implantation is quite tightly timed and takes approximately 48hrs for the egg to burrow into the uterine lining (still hoping that my 2 days pain last week were that '48hrs'!!). HCG cannot be detected until implantation has occured. However, it is specialised cells called trophoblast cells which actually do the secreting (later form the placenta) and this trophoblastic layer doesn't fully establish straight away. Apparently first response is the most sensitive HPT, detecting levels down to 6mIU of HCG, whereas clear blue is 25mIU and the others are 50-100 and above. So, I rekon with a very sensitive test, HCG levels could be detected a few days after the 48hr implantation period. But of course, it varies between women. Sorry about all the regurgitation of info, I'm a bit of a science geek!!! Hope this helps. How long did you get your cramps for?xxxx