I know many people are skeptical about opks working for hpt but they really do and they seem to detect it sooner than hpt. LH and HCG are so similar that opks can detect HCG but not vice versa. If you have spare opks but no hpt you can use them for detecting HCG. You just need to test over a few days and see if the lines get darker and darker, you much also be absolutely positive that you have already ovulated. Here are what my progression lines looked like, the 1st picture is my ovulation, the 2nd is OPK for HPT, and the 3rd is my HPTs.