Understanding False Positives and Negatives in STI Testing

By Dr. Diana Rangaves

Getting tested for STIs is one of the most effective ways to protect your health and your partner’s. However, like any medical test, STI screenings aren’t perfect. Sometimes, results can be misleading. That’s why it’s important to understand what false positives and false negatives are, and how they can impact your testing experience.

Here, we’ll explain what these terms mean, why they happen, and what to do if you ever receive confusing results.

What Are False Positives and False Negatives?

When understanding false positives and negatives in STI testing, the terms might sound intimidating, but they simply describe when a test result doesn’t match reality:

• False Positive: This happens when a test result says you have an infection, but you actually don’t.

• False Negative: This is the opposite. Your test comes back as “all clear,” but you do have the infection.

It may feel unsettling to think about, but it’s important to remember: no medical test is 100% perfect. The good news is that today’s STI tests are designed to be highly accurate, so most of the time, your results are correct.

Still, understanding that false results can happen helps you make sense of your experience and decide on your next steps with confidence.

Why Do False Results Happen?

If STI tests are designed to be accurate, you might wonder why a false result happens at all. There are a few reasons:

• Timing of the test: Many STIs have a “window period,” the time between when you’re exposed and when a test can reliably detect the infection. If you test too soon, your body may not have produced enough markers (like antibodies or viral material) for the test to pick up. This can sometimes lead to a false negative.

• Test sensitivity and specificity: Every medical test has built-in limits. Sensitivity is how well a test detects people who actually have the infection, while specificity is how well it rules out those who don’t. If sensitivity isn’t perfect, you may get a false negative. If specificity isn’t perfect, you may get a false positive.

• Sample quality: Inaccurate results can happen if the sample wasn’t collected, stored, or processed properly. For example, not following instructions for a swab or urine test might affect accuracy.

• Individual health factors: Certain aspects of your health, such as existing conditions, recent vaccines, or medications, can sometimes affect STI test accuracy. For example, antiretroviral drugs used to treat or prevent HIV have been linked to occasional false negatives, even after the window period has passed. In rare cases, interference from antibodies in the blood (known as immunoassay interference) may also cause results to appear inaccurate.

So sometimes, a false result doesn’t mean the test is “bad”—it just means some factors can influence accuracy. Knowing this helps you put your results into context and know when a follow-up might be helpful.

What to Do If You Get a Confusing Result

Getting an STI test result that doesn’t match how you feel can be stressful, but it doesn’t have to leave you stuck. Here are a few steps that can help:

• Don’t panic: A single test result isn’t the whole story. False positives and negatives can happen, so it’s important not to jump to conclusions.

• Consider retesting: If you tested very soon after a possible exposure, or if your result doesn’t match your symptoms, taking another test after the recommended window period can provide clarity.

• Talk with a healthcare provider: A provider can help interpret your results in the context of your health history, symptoms, and risk factors. They may recommend additional testing or treatment.

• Be open with partners: If you’re unsure about your results, it’s okay to pause sexual activity or have an honest conversation with your partner(s) until you get clarity. This step protects both you and them.

How to Reduce the Chances of False Results

While no test is perfect, you can take steps to make sure your STI results are as accurate as possible:

• Test at the right time: Wait until the window period has passed after a potential exposure. Testing too early increases the chance of a false negative.

• Follow instructions carefully: Whether it’s a swab, urine, or blood test, proper sample collection matters. Read and follow the directions step by step.

• Choose reliable testing options: Use certified labs or trusted at-home test providers. Quality matters when it comes to accuracy.

• Share your medical history: Let your provider know about recent exposures, symptoms, or medications you’re taking. This context can help them choose the most accurate test and interpret results correctly.

• Make testing a regular habit: Regular STI testing as part of your routine healthcare can help catch infections early and provide consistent reassurance over time.

Taking these steps won’t eliminate the small chance of a false result, but they will significantly improve the accuracy and reliability of your testing experience.

Clarity Brings Confidence

False positives and negatives can be confusing, but they don’t take away from the importance of STI testing. Knowing they’re possible helps you stay informed and confident about your next steps.

Fortunately, STI testing today is more reliable than ever, offering clear results when you need them most. With at-home STI tests from Everlywell, you get discreet sample collection and accurate results you can trust.

Order your Everlywell at-home STI test today.

References

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3. STI Screening Timetable [Internet]. Eugene, OR: University Health Center, University of Oregon. Accessed September 8, 2025. https://health.uoregon.edu/sites/default/files/STI_screening_timetable.pdf.

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