The problem with using an opk as a hpt is this: a positive opk can tell you three different things
1. You are ovulating
2. You might be pg
3. It's picking up a type of hormone, but not necessarily the hcg you are looking for
It's tempting, I know cause I am a poas addict myself and recently tried. So now I don't know if I am pg or ovulating soon. Best thing to do is get an hpt.
Good luck! Xx