False negative pregnancy test and false positive pregnancy test results explained

Nothing in this article is or should be construed as medical advice; for any medical questions, consult your healthcare professional. 

You stare at your home pregnancy test and can’t help but wonder: Is this right? Maybe it’s negative and your gut is telling you you’re pregnant. Maybe it’s positive and you find this unbelievable. These feelings are normal.

All Clearblue^® pregnancy tests are over 99% accurate from the day you expect your period.¹ False positives rarely occur, and are often due to medical conditions or certain medications. False negatives, while more common, typically occur due to testing too early or drinking too much liquid before testing. Let’s explore this some more.

What can cause a false negative pregnancy test result?

Perhaps you’re more tired than usual, you’re a bit crampy and you swear your breasts feel tender. If you’re holding a negative pregnancy test, you’re probably wondering: Is this right? Rest assured that if you tested from the day you expect your period, your Clearblue^® test is over 99% accurate.¹ Test again in 3 days’ time, as you may have miscalculated when your period is due.

However, false negatives can happen and are usually caused by one of the following factors:

Timing

If you’re testing early, you may have undetectable levels of the pregnancy hormone hCG (human Chorionic Gonadotropin) in your urine, which is what home pregnancy tests detect to determine whether you’re pregnant. Clearblue^® Early Detection Pregnancy Test provides early detection of hCG. 77% of pregnancies can be detected six days before the missed period (five days before the expected period). With each day closer to the expected period, the pregnancy detection rate increases.

What to do if you suspect timing is an issue: If you use any Clearblue® pregnancy test before the day you expect your period and get a “not pregnant” result, test again three days later, as the level of hCG rises rapidly in early pregnancy.² If your tests continue to be negative, and your period is now late, see your healthcare professional.

Your period

It can be easy to miscalculate the expected date of your period. While typical cycle length is thought to be 28 days, this varies among people and between cycles. In a 2020 Clearblue® study of 32,595 women, only 12.4% had a cycle length of 28 days.³ Up to one in three women will, at some point, experience irregular menstrual cycles, especially when they first start their period and in perimenopause.⁴ 

What to do if you suspect you miscalculated your period start date: Visit your healthcare professional if you have cycles that go beyond 35 days or last  21 days or fewer.⁵ There are many causes of irregular cycles including PCOS, stress, excessive exercise, thyroid issues, polyps and fibroids, perimenopause and more.^5,6 Starting and stopping hormonal birth control, including IUDs, can affect your menstrual cycle as well.⁵

Your urine

If you have pregnancy symptoms but a negative test result, you may want to consider, of all things, your pee — especially if you tested early.

What to do if you think your pee may have been a problem: Try again first thing in the morning (or after your longest sleep), when your urine is most concentrated. It’s also important not to drink too much liquid before taking any home pregnancy test, no matter when you take it.

Mistakes

Even though Clearblue^® pregnancy tests are designed for easy use, sometimes unexpected things happen. You may accidentally knock over the container holding your urine sample. Or you may inadvertently let the urine level go above the plastic housing of the test stick.

What to do if you made a mistake: Reread the instruction leaflet carefully and test again with a new test if you get a test error or think you may have tested incorrectly.

Ectopic pregnancy

An ectopic pregnancy is a medical emergency. According to The American College of Obstetricians and Gynecologists, signs of an ectopic pregnancy include lower back pain, pain or cramping in your pelvis or abdomen that’s mild in nature, and vaginal bleeding that’s not normal for you.⁷ With time, you may experience pain in your pelvis or abdomen that comes on suddenly and is severe, as well as shoulder pain.⁷ You may also feel weak and dizzy.⁷

What to do if you have signs of an ectopic pregnancy: Seek help from a healthcare professional immediately.

What can cause a false positive pregnancy test result?

If you’ve been trying to get pregnant, the mere thought of a false positive can be discouraging. But remember: False positives are rare. Pregnancy tests work by detecting the pregnancy hormone hCG. Only a few things can cause people to have detectable levels of hCG not related to pregnancy:

A recent pregnancy

If you’ve had a recent birth, miscarriage or termination, hCG levels can linger for up to 60 days.⁸ So, if you’re testing soon after one of these events, you may get a false positive if your test detects the remaining hCG levels from that recent pregnancy.

What to do if you’ve had a recent pregnancy: Talk to your healthcare professional. They can give you guidance on whether you need to come in for a visit or when to test again.

Early pregnancy loss

It’s also possible to get a positive test result and then find out later you are no longer pregnant, which can be heartbreaking. These are not false positives — they are true positive results even though the pregnancy doesn’t continue.

What to do if you suspect an early pregnancy loss: If you think you are experiencing an early pregnancy loss, contact your healthcare professional. Navigating this unexpected turn of events can be difficult, and you may feel a wide range of emotions. First, know you’re not alone. Many people experience early pregnancy loss.⁹ Also, you may find some comfort in the fact that most go on to have successful pregnancies following an early pregnancy loss.⁹

Medications

Medications containing hCG, such as some fertility treatments, can lead to false positives. The test should NOT be affected by hormone therapies containing clomiphene citrate, common painkillers, alcohol, antibiotics or the contraceptive pill.

What to do if you wonder if your medication may be interfering: Always read the manufacturers’ instructions for any medication you are taking before testing. If you get unexpected results, you should discuss them with your healthcare professional.

Medical conditions

In some rare cases, certain medical conditions can cause a rise in hCG levels, even if you’re not pregnant. These include certain cancers.⁸

What to do if you are concerned about a possible medical condition: Talk to your healthcare professional. Additional testing can help determine why hCG is present.⁸

Perimenopause

A very small number of non-pregnant women may have low levels of hCG during the menopause transition.² Perimenopause can begin anytime between the ages of 40 and 58.¹⁰

What to do if you think you are in perimenopause: Talk to your healthcare professional. Additionally, consider using the Clearblue® Early Detection Pregnancy Test, which features DualSense™ Technology that may help prevent false positives from non-pregnancy related hCG in the very small number of non-pregnant women who may have low levels of hCG in their urine. The Clearblue® Menopause Stage Indicator is another resource for navigating this period in your reproductive journey.

We know that the idea of a false negative or a false positive can be worrisome. But here’s the bottom line: If your period is due and you use a Clearblue® pregnancy test, following the instructions carefully, the result will be over 99% accurate.¹ If your test result is negative and your period is late, test again three days later or see your healthcare professional.

Related Articles

• Do pregnancy tests expire
• How many pregnancy tests should you take?
• In-office pregnancy testing vs. home pregnancy testing: What’s the difference?

Stay in-the-know with the Clearblue® blog

Looking for insights on your health journey? Clearblue® sends you curated, science-backed articles right to your inbox.