Home pregnancy
tests work by detecting the presence of Human Chorionic Gonadotropin,
HCG. Today's home pregnancy tests can detect HCG in the urine
of pregnant women even before a period is missed.
If OPKs
detect LH and HPTs (home pregnancy tests) detect HCG, why
would anyone think you could use an OPK as an HPT?
HCG and
LH
Let's
take a closer look at LH and HCG. Both hormones are glycoproteins,
meaning they consist of a protein with a sugar attached to
it. If you remember from high school biology, proteins can
be broken down into chains of amino acids. HCG and LH can
be broken up into two units or "chains", one subunit
called alpha and the other beta. If you look at the alpha
subunit, the chains of amino acids are identical. In fact,
HCG's alpha subunit is identical to the hormones LH, FSH,
and TSH, all produced in the pituitary gland. HCG is the only
one of these alpha subunits that is not produced by the pituitary,
but rather the placenta.
We know
that the alpha subunits are identical, but what about the
beta subunits? The beta subunits of LH and HCG are also very
similar in structure. Not only are they similar in structure,
they are also similar in function. This is why you will see
HCG injections used as an infertility treatment. HCG injections
are used to replicate the LH surge of the menstrual cycle
to induce ovulation.
Where
HCG and LH differ is HCG's beta subunit has about 30 extra
amino acids attached to the end of it. Home pregnancy tests
are designed to specifically look for this HCG beta subunit.
OPKs
as HPTs
OPKs are
intended to detect LH. Since LH and HCG are nearly identical,
OPKs will also detect HCG. The reverse is not true for HPTs.
Home pregnancy tests will only detect HCG. So in theory, yes,
and OPK could detect pregnancy.
Reasons
not to use an ovulation prediction kit for a home pregnancy
test
OPKs cannot
distinguish between LH and HCG. Getting a positive OPK only
confirms that you have either LH or HCG in your system.
It is
important to discuss some of the other differences between
OPKs and HPTs. LH is present in the body at all times. HCG
is not. WIth OPKs, they detect a sudden increase or "surge"
of LH. The typical amount of LH that is in the body at any
given time is between 5-20 mIU. Therefore an OPK is looking
for a surge above this typical amount. Most OPKs look for
a level around 30-40 mIU. However, there are some tests that
detect lower levels of LH. You can easily see how testing
with a more sensitive OPK could result in a false positive.
Newer OPKs look at a combination of LH and estrone-3-glucuronide,
E3G, which may be helpful to further pinpoint ovulation.
Home pregnancy
tests on the market are very sensitive testing at 25 mIU and
below. This is more sensitive that the typical OPK. So even
if you could get a positive on an OPKs, you would most likely
get one sooner on a home pregnancy test. Because OPKs are
designed to detect LH and not HCG , it is not recommended
to use an OPK for an HPT.
