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Wondering if a false positive on an ovulation test is an urban fertility myth? Well, spoiler: it’s not!
Yes, ovulation tests can be invaluable when you’re trying for a baby. They pinpoint when you’re most fertile, so you know when to do the deed for the best chance of pregnancy.
But while helpful, they can be confusing and frustrating. Especially if you’re not aware of their quirks or limitations.
In this article, we’ll break down how OPKs work, six reasons you may get a false positive, and how to get the most accurate results.
What are OPKs?
Ovulation tests, also called ovulation predictor kits (or OPKS), do just what the name suggests – they predict ovulation. They do this by detecting luteinizing hormone (LH) in your urine.
Around 24-36 hours before you ovulate, LH surges. This triggers the follicle to open up and release the mature egg.
Once released, an egg survives for roughly 12-24 hours. That’s why knowing when you’re ovulating is crucial when you’re trying to get pregnant.
That way you can time sex on the days you’re most fertile, so you have the best chance of conception.
How Do OPKs Work?
Ovulation tests measure how much LH is in your urine. Most OPKs base their results on average thresholds. That means they only detect LH levels above 25-30 mIU/mL. If your LH passes that amount, you get a positive result.
Most ovulation predictor kits come with two lines: a control line and a test line. The control just shows the test is working. The test line is what gives your result.
The trouble is, reading ovulation kits can be tricky.
What Do Positive Results Look Like on OPKS?
Reading a pregnancy test is plain as day. Two lines = you’re pregnant! But OPKs aren’t so cut and dry.
For a positive OPK, the test line must be at least as dark as the control line, or darker. If an OPK detects a small amount of LH in your urine, the test line may show up as a faint line.
However, a faint line does not equal a positive ovulation test. It means LH was detected but isn’t at surge levels.
This could also mean LH hasn’t spiked yet – or that the surge already passed. You can read more about faint lines here.
Along with LH, some ovulation tests measure estrogen as well. This is because estrogen rises about three days before you ovulate.
Knowing when your estrogen is rising gives you a better prediction of your fertile window.
That’s because sperm can survive for up to 4-5 days. So the more sperm in your body when an egg drops, the better your chances of conceiving.
Learn more: Positive Ovulation Test: How Long Am I Fertile After a Positive Ovulation Test?
What Causes a False Positive Ovulation Test?
When used correctly, ovulation tests predict the LH surge with up to 95% accuracy. However, an LH surge can only predict ovulation and doesn’t always guarantee ovulation.
And since LH surges vary, some OPKs may not be sensitive enough to pick up your surge. Certain health conditions like PCOS can also muck up your results on OPKs.
So without further ado, here are six reasons false positives happen:
1. Anovulatory Cycles
It is possible that your LH surged, but it did not trigger ovulation. This can result in anovulation. The surge in LH can give you a false positive result on your OPK.
It’s not uncommon to have an anovulatory cycle now and then. But chronic anovulation can cause fertility problems.
2. LH surge type
It was once believed that all LH surges were short with one dramatic peak. But that’s not the case. LH surges vary by their onset and pattern. And the type of surge you have will affect your OPK results.
For example, only 42.9% of LH surges are rapid, meaning they’re over within a day. If you have a short surge, you could get a positive ovulation test in the morning and a negative one that night.
Around 57.1% of women have gradual surges that stretch out over 2-6 days. In this case, LH will stay high for the length of your surge. That means you’d get positive results several days in a row. This also depends on the type of gradual onset surge you have:
Biphasic Surge
About 44.2% of women have biphasic surges, meaning LH spikes twice. If you have a double surge, an OPK may show a positive result for both spikes.
Plateau Surge
Around 13.9% of surges follow a plateau pattern, meaning LH peaks and stays high for several days. If you have this surge pattern, you may get a positive OPK for the entire plateau.
3. Alpha Beta Cross-reactivity
Hormones like LH, FSH, hCG, and TSH are made up of beta and alpha subunits. Their alpha subunits are identical. But their beta subunits give each hormone its unique characteristics.
Here’s the problem – many ovulation predictor kits measure alpha LH. This may lead to cross-reactivity, meaning the test detects FSH, hCG, or TSH but reads it as LH. This can lead to false positive results.
Or when someone takes an hCG trigger shot to induce ovulation, the OPKs read it as LH and give you a false positive result.
One easy way to avoid this is to choose an ovulation test that measures beta LH, like Inito. Since beta subunits are distinct, there’s less chance for cross-reacti
4. Polycystic ovary syndrome (PCOS)
PCOS is a hormonal imbalance marked by high levels of androgens. This throws off other hormones, including luteinizing hormone (LH).
Women with PCOS often have high LH levels non stop. This can result in ovulation for some, but for many, that’s not the case. Sometimes ovulation just doesn’t occur due to the high LH levels. This gives you a false positive result on an OPK for many days. But you ovulate only once during your entire cycle.
5. Prescription drugs
According to the American Pregnancy Association, the following medications may throw off your ovulation test results:
- Pergonal
- Danazol
- hCG injections
- Clomid
- Serophene
Some of these drugs help stimulate ovulation, while others suppress ovarian function. Either way, they can lead to inaccurate results.
If you’re trying to conceive and are taking any of these medications, talk with your doctor before using an OPK. They can recommend when to start testing to get the best accuracy.
6. Pregnancy
If you’re pregnant or were recently pregnant, this can interfere with your results on OPKs.
When you’re pregnant, your body produces the human chorionic gonadotropin hormone (hCG). Pregnancy tests detect hCG in your pee to deliver a positive result.
hCG has a structure that’s very similar to LH. So much so, that some ovulation predictor kits mistake hCG for LH. This can lead to a false positive result.
How Do I Avoid False Positives?
You can reduce your risk of getting a false positive with these tips:
Test correctly
For the most accurate results, follow these best practices:
- Check the expiration date. If the ovulation kit has expired, toss it and get a new one.
- Test twice a day. If you have a quick LH surge and test once a day, you could miss it.
- Follow the instructions exactly. Each OPK will vary somewhat.
- Test with your second-morning urine. LH surges usually happen between midnight and 8 am. But it can take 3-6 hours to show up in your pee.
- Avoid drinking a lot of water before testing. This may dilute your urine and skew your results.
- Try not to pee for 4 hours before taking the test. That way LH will be more concentrated in your pee.
Keep in mind, if you’re getting a false positive due to the problems mentioned above, these tips won’t change that.
However, testing correctly can give you peace of mind that a false positive isn’t due to faulty testing.
Use a digital test
Reading ovulation test strips can be confusing. You may not be able to tell whether the test line is dark enough to indicate a positive test result.
One easy way to avoid this is to choose a digital test.
Digital tests are way easier to read. Instead of wracking your brain analyzing how dark the test line is, you get clear-cut results (like a happy face or the word ‘fertile’). That said, there is still a risk of cross reactivity if your digital test measures alpha LH.
Track PdG along with LH
It’s possible for LH to surge and still not ovulate. Remember, the rise in LH predicts ovulation. But it doesn’t guarantee it.
To confirm ovulation, you’ll want to track PdG. This is a metabolite of progesterone, which rises just after an egg is released. If you see PdG shoot up after LH surges, you can rest easy that ovulation occurred.
To know more about different scenarios of anovulation, check this.
What Should I Do If I Get a False Positive?
The best way to know when you’re ovulating is to track your hormones. The better you understand your cycle, the better your chances of getting pregnant.
FSH, estrogen, and LH all help predict your 6-day fertile window. And progesterone’s rise is what confirms ovulation.
Try using the Inito Fertility Monitor, which measures your LH, FSH, estrogen, and PdG (urine metabolite of progesterone) all in a single test strip. Tracking this foursome gives you a clearer picture of your entire fertility window. But it also confirms ovulation really happened. Inito also tests beta LH, so there’s less risk of cross-reactions.
Read more about ovulation symptoms here.
Ovulation Testing FAQs
Ovulation tests can bring up a lot of answered questions. So, let’s clear some of them up:
How long will an ovulation test stay positive?
That depends on the length of your LH surge. Women with short surges may get a positive result one day and a negative result the next. But if you have a gradual surge, you may get a positive test result for up to 6 days.
Can sperm cause a false positive?
No. Ovulation tests base results on your hormone levels. So, sperm will not affect your results. However, semen may probably cause a false positive since it has some amount of LH. Although there is no evidence for the same.
What are my chances of getting pregnant after a positive ovulation test?
It depends on which day you have sex in your fertile window. According to one study from Fertility and Sterility, the day before ovulation occurs is your best bet, with a 41% chance of conceiving. To see how the other days in your fertile window stack up, check out this blog post.
Takeaways
- Ovulation predictor kits detect luteinizing hormone (LH) in your urine to tell when you’re approaching ovulation.
- A positive ovulation test result is when the test line looks as dark or darker than the control line.
- False positive results may be due to cross-reactivity, pregnancy, PCOS, prescription drugs, and certain types of LH surges.
- For the best accuracy and to avoid missing the surge, follow the instructions exactly and test twice a day.
- OPKs predict ovulation, but don’t confirm it. Since progesterone rises after an egg is released, tracking PdG can confirm that ovulation occurred.
- Inito measures your LH, FSH, estrogen, and PdG to confirm ovulation and give you a better look at all your fertile days.
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- Urinary Luteinizing Hormone Tests: Which Concentration Threshold Best Predicts Ovulation? – PMC
- (PDF) Development of the first urinary reproductive hormone ranges referenced to independently determined ovulation day
- Breaking Research Reveals That Not All Home Ovulation Tests Are Equally Reliable | AACC.org
- Detection of ovulation, a review of currently available methods – PMC
- Characteristics of the urinary luteinizing hormone surge in young ovulatory women – Fertility and Sterility
- Structure–Function Relationships of Glycoprotein Hormones and Their Subunits’ Ancestors – PMC
- How to Use Ovulation Kits & Fertility Monitors
- Onset of the preovulatory luteinizing hormone surge: diurnal timing and critical follicular prerequisites – Fertility and Sterility
- Findings from a mobile application–based cohort are consistent with established knowledge of the menstrual cycle, fertile window, and conception
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