You Shouldn’t Reuse a Pregnancy Test — Here’s Why

Spend any length of time browsing TTC (trying to conceive) message boards or chatting with friends deep into their own pregnancy journeys and you’ll notice that home pregnancy tests (HPTs) can be unpredictable.

Among the factors that can influence an HPT’s reliability are:

• evaporation lines
• expired tests
• storage or exposure to moisture
• time of day
• how hydrated you are
• color of dye (pro tip from a HealthEH reader: pink dye pregnancy test options tend to be preferable)
• how long you waited after urinating to check the outcome
• whether the wind speed is precisely 7 miles per hour east-southeast (OK, we’re joking about this last one, but when you’re TTC it can sure feel like every little detail matters)

Short version: These tests are sensitive to lots of variables. While they do a good job detecting the pregnancy hormone human chorionic gonadotropin (hCG), getting a trustworthy result depends on following the package directions exactly.

So no — you can’t reuse a pregnancy test. Here’s a closer look at why that is.

How HPTs function

The exact formula manufacturers use to detect hCG is proprietary, but the basic principle is the same: a chemical reaction happens between your urine and the hCG antibodies embedded in the test strip. Once that reaction occurs, it cannot be repeated.

This applies to digital tests as well. Even if you don’t see colored lines, there’s still a reactive strip inside the device. The digital portion merely interprets the strip and shows the result on a screen. So digital tests aren’t reusable either.

Typically, you should read your pregnancy test about 5 minutes after you POAS (pee on a stick in TTC-speak) or dip the strip in urine and then discard it — and don’t dig it out of the trash an hour later! (Evaporation can create a second line by then, possibly producing a confusing and upsetting false positive.)

Why reusing a test can create false positives

If you remember even a smidge of high school chemistry, reactions between two substances generally happen once. To run the same reaction again, you need fresh reagents.

When your urine contacts an HPT — whether you hold the stick in your stream or dip it into a collected sample — that reaction takes place and is finished. (Think of a popcorn kernel: once it’s popped you can’t pop the same kernel again. You need a new one.)

What if you open a discarded test and it gets splashed with plain water?

Keep in mind water is still composed of elements — hydrogen and oxygen — and can interact with the test strip. Water will likely yield a negative result, but you still shouldn’t then add urine to that same strip.

If you reuse a strip that’s already been wetted — by water or urine, even if it has dried — you may see a false positive.

That happens because as an HPT surface dries, an evaporation line can form. While that line is often colorless, adding moisture later can cause dye to accumulate in the evap line and mimic a true positive.

Additionally, a used test is regarded as finished. Any result from attempting to use it again should be treated as unreliable.

How to use an HPT for the most reliable outcome

Always follow the instructions on the box. However, this common routine applies to many mainstream brands:

1. Wash your hands. If you plan to use the cup method, clean a cup with hot, soapy water first.
2. Unwrap an individual test and set it on a clean, dry surface near the toilet.
3. Pick your approach: For the cup method, begin urinating, pause mid-stream and place the cup, then resume to collect enough urine for dipping (don’t submerge). Dip the tip of the test (not past the max line) into the cup for roughly 5 seconds. For the mid-stream method, start peeing and hold the test in your stream for about 5 seconds.
4. Walk away and let the chemical reaction run its course.
5. Return to read the test about 5 minutes later. (Don’t wait more than 10 minutes — beyond 10 minutes results may be invalid.)

Again, check the specific brand directions, as some tests differ.

Bottom line

It can be tempting to reuse a pregnancy test — especially if you’re convinced a negative is wrong, if it only got slightly wet, or if it’s dried and you’ve run out of tests.

But resist that urge: tests aren’t reliable after they’ve been wetted, either by urine or water.

If your test is negative and you still suspect pregnancy, be patient. hCG can take time to reach detectable levels. Dispose of the used test, try to distract yourself from TTC stress, and test again with a fresh strip in a couple of days.