Can Pregnancy Test Cards Give False Results? Debunking Common Myths

You bought a pregnancy test card. You waited the few minutes. One line. Two lines. Your heart skips. Then you start doubting: Could this be wrong? You’re not alone. Thousands of people second-guess their results every month. And for good reason-there’s so much noise out there. Myths about evaporation lines, expired tests, and drinking too much water before testing are everywhere. But here’s the truth: pregnancy test cards are accurate most of the time. Still, they can give false results-and knowing why matters more than ever.

How pregnancy test cards actually work

Pregnancy test cards detect one hormone: hCG. That’s human chorionic gonadotropin. It’s made by the placenta after a fertilized egg attaches to the uterus. Most test cards can spot hCG as low as 20 mIU/mL. That’s usually around the time your period is due. Some ultra-sensitive ones go as low as 10 mIU/mL, which means they can pick up pregnancy a few days earlier.

Inside the test card is a strip coated with antibodies that stick to hCG. When your urine flows over it, those antibodies grab any hCG present. Then a chemical reaction shows up as a colored line. One line? Negative. Two lines? Positive. Simple. But simplicity doesn’t mean perfection.

False negatives: When the test says no, but you’re pregnant

False negatives happen more often than false positives. And they’re usually due to timing. If you test too early, your hCG levels might be too low for the test to catch. A 2023 study in the Journal of Obstetrics and Gynecology found that 1 in 5 women who tested negative on the first day of a missed period were actually pregnant-when tested again a week later.

Other reasons:

• You drank a lot of water before testing. Diluted urine = lower hCG concentration.
• You didn’t follow the instructions. Waiting too long to read the result? That’s a common mistake.
• The test is old or damaged. Exposure to heat, moisture, or direct sunlight can ruin the chemicals inside.
• You have a very early miscarriage-sometimes called a chemical pregnancy. hCG rises briefly, then drops fast. The test might catch it, then turn negative soon after.

Bottom line: If your period doesn’t come and the test says negative, wait 3-5 days and test again. Use first-morning urine. It’s the most concentrated.

False positives: When the test says yes, but you’re not pregnant

False positives are rare-under 1% of cases-but they do happen. And they’re scary. You might see two lines and assume you’re pregnant, only to find out later you’re not.

Here’s what can cause it:

• You recently had a miscarriage or abortion. hCG can linger in your system for weeks.
• You’re taking fertility drugs that contain hCG. Some injections, like Ovidrel or Pregnyl, are designed to trigger ovulation-and they can mess with test results for up to 10 days after use.
• You have a medical condition. Rare tumors, like gestational trophoblastic disease or certain ovarian cancers, can produce hCG.
• You have a faulty test. Manufacturing errors happen. A test might have a defective strip or contamination.

Evaporation lines are often blamed. But they’re not true positives. They’re faint, colorless streaks that appear after the recommended reading time (usually 10 minutes). If you see a line after 15 minutes, it doesn’t count. Always read the result within the time window on the box.

Expired or improperly stored tests: The silent saboteurs

Most people don’t check the expiration date. Or they store the test in the bathroom-right next to the shower. Humidity and heat break down the antibodies inside the test card. A 2024 lab test by Consumer Reports found that tests stored at 90°F (32°C) for 6 months lost up to 40% of their sensitivity.

Always store pregnancy tests in a cool, dry place. A drawer, not a medicine cabinet. Check the date. If it’s expired, throw it out. Don’t risk it.

Medications and medical conditions that interfere

Most common meds-birth control pills, antibiotics, painkillers-don’t affect pregnancy tests. But some do.

• HCG injections for fertility treatments: These are the biggest culprits. If you’re undergoing IVF or ovulation induction, your doctor should tell you when it’s safe to test.
• Pituitary disorders: Rare conditions like hypergonadotropic hypogonadism can cause elevated hCG without pregnancy.
• Menopause: In rare cases, postmenopausal women produce trace amounts of hCG. This can cause false positives in older women who aren’t aware of this possibility.

If you’re on any hormone therapy or have a history of cancer, talk to your doctor before trusting a home test. Blood tests are more accurate and can distinguish between different types of hCG.

When to trust the test-and when to see a doctor

Here’s a simple rule: If you get a positive result, believe it. Even if you feel nothing, even if you’re not sure. A true positive is almost always real.

But if you get a negative result and your period still hasn’t come after a week, test again. Or better yet, go to a clinic. A blood test can measure exact hCG levels and confirm pregnancy with 99% accuracy. It can also catch early problems-like ectopic pregnancy or low hCG progression-that a home test can’t.

Don’t wait for symptoms. Some women have no morning sickness, no breast tenderness, no fatigue-and still have a healthy pregnancy. Others feel everything and aren’t pregnant. Symptoms aren’t reliable. Only hCG is.

What to do if you’re confused by your results

Follow this checklist:

1. Check the expiration date.
2. Use first-morning urine.
3. Wait the full time (usually 3-5 minutes) before reading.
4. Don’t read results after 10 minutes.
5. Use a new test if you’re unsure.
6. If still confused, get a blood test.

Keep in mind: No home test is 100% perfect. But when used correctly, pregnancy test cards are more than 99% accurate from the day your period is due.

Myth vs. Fact: Quick debunking

• Myth: Drinking lots of water makes the test more accurate.
  Fact: It dilutes hCG. That’s why you get false negatives.
• Myth: A faint line means it’s not real.
  Fact: Any second line, even faint, is a positive. It just means hCG is low.
• Myth: Only expensive tests work.
  Fact: Generic brands are just as accurate if they’re not expired and stored properly.
• Myth: You can’t get pregnant right after your period.
  Fact: Ovulation timing varies. Sperm can live for 5 days. Testing too early is the real issue.

The bottom line? Pregnancy test cards are reliable tools-but they’re not magic. They need to be used right. And they’re not a substitute for medical confirmation when something feels off.

Next steps if you’re unsure

If you’ve tested multiple times and still don’t know where you stand, don’t guess. Don’t wait for symptoms. Don’t rely on online forums. Call your doctor or visit a clinic. A simple blood test costs less than $50 in most places and gives you a number-your exact hCG level. That number tells you more than any line on a plastic card.

And if you’re pregnant? Early prenatal care improves outcomes. If you’re not? You can rule out other causes for your symptoms-like hormonal imbalances, thyroid issues, or stress-related changes.

Pregnancy test cards are tools. Not crystal balls. Use them wisely. And when in doubt, let a professional confirm it.