A dark line on an OPK (darker than the test line) should indicate that ovulation will happen within the next 24-36 hours. Women with PCOS can have higher levels of LH in the body all the time. (normally it's only before ovulation that the hormone LH rises. OPK's look for higher levels of LH than normal) So with women who have consistently higher levels of LH, due to PCOS, can find it harder to use OPK's as the results may be unreliable. If you are having regular period's, there is a good chance that using the OPK will work. In this case, women with PCOS (but normal LH levels) can use the OPK's in the same way as other women. If the line is lighter than the test line you're not ovulating.