Found this roday, really interesting!
A woman trying to conceive asked her doctor if she could use Ovulation Predictor Tests (OPK's) as Home Pregnancy Tests (HPT's). The reason for the question is that it is asked a lot on "trying to conceive" web sites. Many women will have an extra OPK after ovulating and may want to use it as an HPT. Here is what the doctor said.
The chemical make-up of LH (LH is the hormone that triggers the release of the egg and is very high prior to ovulation and causes a positive result on an OPK), is one thread short of being hCG (HCG is produced by the placenta during prenancy and it is what HPT's look for). That is why you will not get a + hpt if you are having your LH surge, but you will get a + OPK if you are pregnant, that one thread that is in the hCG, but missing from the LH is what makes the hpt work.
But on the other hand, he did say that an OPK is probably the most sensitive hpt you can buy. He said that there are two ways to use it.
1. Using it daily and if your test line gets darker then you are most probably pregnant
2. Use it once (yeah right ), and if your test line is as dark as or darker than the referance line then you are pregnant.
He said that the only bad things about using the OPK are that
1. The OPK will pick up a + hCG before the doctor's office test but about two days after a beta test would pick it up (detecting 10mIU of hCG being between 7dpo - 9dpo ~ according to the average impant of 5-7 days), so if you are waiting to take a urine test at the doc's office, you would still have to wait.
2. It detects pregnancy so early that it will detect chemical pregnancy and early m/c pregnancy
3. Cannot be used reliably by PCOS patients if they have a high LH (as most do)
And.....somebody else says:
Way back when, as a grad student, I used to assay cortisol (stress associated hormone) in urine/plasma/saliva, and I can tell you that the amount you can get from a saliva sample is the toughest to detect - just not a whole lot in there and the pH and digestive enzymes present are a nightmare issue for most people developing new assays that use saliva . . . saliva is what most labs would like to use since it is the easiest to get a sample of . . . a fellow student used to use unused cigarette filters for folks to chew on to get as much saliva as possible - they then had to centrifuge the filters to spin out all the saliva in to a tube to get as much as they could . . .
OPKs don't have the same quality control that HPTs have. LH and HCG share very similar sequence/shape and HPTs contain antibodies that can only detect HCG; but OPKs usually aren't that clean (since they don't have to be) and typically pick-up some HCG in addition to LH.
After my m/c my doc said I could monitor my own HCG levels (dropping) with OPKs since they were cheaper than HPTs and it worked!
.............
Here's the results of one of the many women who tried to use saliva on an HPT. She got a positive with her urine (left) and an even fainter, but still there, positive with her saliva (right). Here here for women conducting laymen scientific experiments!
