You can not and and should not use the OPK ovulation predictor kit as a HPT home pregnancy test.
Each of these two tests checks for a different hormone:
|OPK Ovulation Predictor||Pregnancy Test|
A positive OPK will not tell you with enough certainty that you are pregnant. And if the OPK is negative you could still be pregnant.
When you do a pregnancy test you want a straight answer: Am I pregnant or not? A positive HPT tells you with 99+% certainty that you are pregnant.
Only a positive HPT pregnancy test will give you that answer with certainty, the positive OPK will not give you that answer.
OPKs have a high false positive as well as a high false negative rate for being pregnant. If an OPK is positive you could still NOT be pregnant, and if it's negative you could still BE pregnant.
You should not use one to check for the other.
Coincidentally, you could have a positive OPK, an elevated LH when you are pregnant, but a positive OPK will not confirm the pregnancy. You could have a false positive OPK but not a false positive pregnancy test.
Only a positive pregnancy test tells you that you are pregnant, and if the pregnancy test is positive that's a nearly 100% confirmation you are pregnant.
A positive result on an OPK could mean you are near ovulation, pregnant, or the test is picking up an entirely different hormone or element. Or it may be negative even if a woman is pregnant. With a positive HPT there is no doubt.
OPK's work differently than HPT's. A pregnancy test will develop 2 lines only if hCG (pregnancy hormone) is detected. Thus, "a line is a line" when determining a positive HPT. OPK's work differently. An OPK has a "control" line and a "test" line, just like an HPT. Unlike an HPT, however, the mere presence of a "test" line does not mean the test is positive. The test line must be as dark as, or darker than, the control line to be a positive result (meaning that a surge was detected, rather than the ordinary amount of LH usually found in your urine every day.)
This means that there is already some ambiguity involved in reading an OPK's results. Sometimes the line is almost as dark as the control line, but perhaps not quite as dark. Sometimes only the edge turns dark, or the top half of the line is darker than the bottom.
Additionally, OPK's are not as sensitive as a lot of HPT's are. This means that, if pregnant, you are likely to get a positive HPT earlier than you would get a positive OPK.
On a different note, the OPK is usually more expensive than the pregnancy test. Why use something unreliable and more expensive when you can get the real thing cheaper?