Clairsmummy-I have read that opks can be used as HPT if your AF is due or late but to be honest if the HPT are neg i would disregard the opks as i have had positive opks right up until AF is due as some of them can detect the LH hormone after O and show positive that is why the instructions say once you get your 1st pos on a opk dont test any more but if you are very late it is a good sign my fingers are crossed for you.