For this 2WW, I am conducting an experiment. I have no pregnancy tests in the house. I do however have about a dozen ovulation tests. Ovulation tests (OPK) and pregnancy tests (HPT) differ in several ways.
OPKs detect LH, which is the hormone that surges just before ovulation. A positive test is when the test line is darker than the control line. There may be a faint line all the time, but it isn’t positive until that second line gets dark. The tests I have will detect an LH higher than 20. They never detect levels lower than their stated sensitivity, because you only want to catch the surge in LH. If they were more sensitive, you would get too many false positives since there is always some LH in your system. OPKs will cross react with hCG, because LH and hCG share a common structure, so you can get a positive OPK if you are pregnant.
HPTs detect hCG, which is the hormone that the implanted embryo produces. They only detect hCG not LH (they test for a part of the protein specific to hCG), and since you only have hCG in your system if you are pregnant (or have a tumor, but we’ll just leave that possibility out of the discussion for now) you don’t get false positives. A line is a line. The sensitivity of these varies, but the ones I get claim to detect hCG higher than 25, although some actually detect even lower levels.
Since I have a sick addiction to peeing on small pieces of plastic, I am using the OPKs as a screening test. The ones I have are cheap ones from amazon (about $0.18 each) so I feel ok about this. I would not try this experiment with drug store OPKs ($3 each). My plan is to see if I get a positive OPK, which would suggest my hCG is over 20 (my LH should stay suppressed as long as I keep taking my estrogen). Then I can go buy an HPT and see if it worked. It’s ridiculous, really. But it keeps me occupied and keeps me from taking HPTs too early (Thursday is really the soonest I should expect a positive result).
I will be sure to publish my results at the conclusion of the study. With the way work is going lately, it might be my only experiment worthy of publication.