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Reliability of Home Pregnancy Tests: Are They Accurate or Is a False Positive or False Negative Possible?

Chris Telden knows how fortunate she is to be a mom at all, given her high-risk pregnancy and the challenges of extended breastfeeding.

How Do Home Pregnancy Testing Kits Work?

Using a home pregnancy testing kit is easy; basically, you dampen the testing stick with your urine. A couple of minutes later, the stick changes color, showing a negative result (meaning you're not pregnant) or a positive result (you're pregnant).

Are They Accurate?

These tests are a quick and convenient way to learn whether or not you're pregnant—but how reliable are they? The short answer is:

  • For positive results, they're quite accurate overall.*
  • For negative results, their reliability and accuracy are not as dependable.

Available in pharmacies and drugstores, over-the-counter home pregnancy tests work by detecting the presence of hCG, also known as "the pregnancy hormone," in your urine. hCG is only around if you're pregnant.

If you get a positive result on a home pregnancy test, that means it found the hormone—in which case, well, it found the hormone, and you're very likely pregnant.

If you get a negative result, that means the test didn't find the pregnancy hormone. It may not have found it because you're not pregnant, but it also may not have found it because not enough hCG has built up in your body yet. A false positive result is less likely when you use a home pregnancy kit than a false negative result.

*This only applies to authentic test kits. For years this article has had extra visits around April Fool's Day - suggesting prank kits showing false positives are out there.

Most home pregnancy tests are reliable if used correctly.  Photo Courtesy of wickedchimp under Creative Commons Attribution License

Most home pregnancy tests are reliable if used correctly. Photo Courtesy of wickedchimp under Creative Commons Attribution License

Ensuring the Accuracy of a Home Pregnancy Test

According to the National Women's Health and Information Center, home pregnancy tests, when used properly, give extremely accurate results. Some tips to ensure accuracy include:

  • Follow the directions on the pregnancy kit. Follow both sampling instructions and timing instructions to the letter.
  • Take the test in the morning, when the concentration of hCG tends to be greater.
  • Don't drink anything right before taking the test, so as not to dilute the concentration of the pregnancy hormone in your urine, if present.
  • Discard test kits that have expired dates.
  • Study the test results key to make sure you're interpreting the colors and patterns on your test strip accurately.
  • Test yourself with the home pregnancy kit at least a week after your missed period.

Why Should You Wait to Take a Home Pregnancy Test Until a Week After Your Missed Menstrual Cycle?

All pregnant women produce hCG (human chorionic gonadotropin) when they're pregnant. The hormone first appears in very low concentrations about 6 days after conception. Every day after this, the concentration increases, until there's so much of it that a home pregnancy test can reliably detect it.

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If you do take the test earlier and get a positive result, it's probably a true positive - the test was simply sensitive enough to detect trace amounts of hCG in your urine.

Don't trust a negative result from a test you took less than one week after your missed period, however. Ten percent of women experience delayed conception, so it's a good idea to follow a negative result with a repeated test a few days later.

If you do need to know whether you are pregnant before a home test kit can accurately tell you, then the Mayo Clinic advises that you go to your doctor and ask for a blood test to check for pregnancy.

Reliability of Home Pregnancy Test Kits and Specific Brands

Some home pregnancy test kits claim to be accurate and reliable when testing on the day you miss your period. They may be sensitive enough to do so, but it depends largely on what levels of pregnancy hormone you have in your urine—it varies from woman to woman.

The designs of the kits vary. They all do the same thing—try to detect the pregnancy hormone—but some use test strips, others powders, and some are more sensitive than others during early pregnancy.

The First Response, Early Result Pregnancy Test, in a comparison with 17 other home pregnancy tests, was found in a 2004 study to accurately detect low hCG levels quite early on. But if you're testing for pregnancy at home after about seven days after your missed period, most test kits are accurate if they show a positive result (pregnant).

How Common Are False Positives / False Negatives on Home Pregnancy Tests?

As long as the expiration date isn't expired and the test isn't defective, you're unlikely to get a false positive result, according to the Mayo Clinic. There is a small chance that traces of some medications, protein, or blood in your urine could yield a false positive, but this is unlikely. Check with your doctor if you are unsure.

False negatives do commonly occur, generally either because of taking the pregnancy test before your level of hCG is high enough to be detected, or not following the timing instructions on the test. If you've missed your period and there's a chance you might be pregnant, it's best not to assume a negative result is conclusive.

I Got a Positive Pregnancy Test Result: Now What?

It's time to call your doctor. Your doctor will perform a blood test and maybe a pelvic exam to confirm the pregnancy—you'll find out the results right there in the doctor's office. If you're pregnant, then you need to get started with your prenatal care.

If you got a negative result, but you've had missed periods, then it's a good idea to call your doctor anyway, to see what's going on and if there's a medical problem you should know about.

This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

Questions & Answers

Question: I got 4 positive pregnancy tests, then 4 negative. What should I do?

Answer: Since you got several of both, I'd check with my doc for sure.

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