So ladies for those of you asking if you can use an OPK as a HPT. I'd say the answer is yes. If you don't have an HPT available to you and it does take a lot of hcg. But mine did not turn positive until after I got a positive on an HPT. Two days ago I took an HPT and OPK together the OPK was negative they HPT was positive. Today I took an HPT and OPK together and they were both positive. I'm 13 Dpo. It's one day before my expected period.