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What’s the Difference Between Screening and Diagnostic Testing for STIs?

  • Writer: Trusti Team
    Trusti Team
  • Apr 15
  • 3 min read

If you've ever gone for an STI test and been confused about why the doctor called it a "screening" instead of a "diagnostic test," you're not alone. Medical jargon can make a simple visit to the clinic feel like a pop quiz you didn’t study for. But fear not! We’re here to break down everything you need to know.


Screening vs. Diagnostic Testing: The Basics

At first glance, STI screening and diagnostic testing might seem interchangeable. After all, they both involve getting tested for sexually transmitted infections. However, they serve different purposes:

  • Screening is for people who don’t have symptoms but want to check for STIs. Just a routine check-up to make sure that you're safe and sound.

  • Diagnostic testing is for people who do have symptoms or have been exposed to an STI. Definitely not as routine as screening, but a necessary test for those who need it.


Both types of tests are essential, but knowing which one applies to you can help you navigate the world of STI testing with confidence.


Screening: The Preventative Approach

Screening is all about catching STIs before they cause complications. Since many STIs don’t show symptoms right away (or at all), routine screening is crucial for sexually active individuals.


According to the Centers for Disease Control and Prevention (CDC):

  • Around 70% of women and 50% of men with chlamydia don’t experience symptoms.

  • Nearly 90% of people with genital herpes don’t know they have it.


This means that waiting until you have symptoms is like waiting for your car to break down before checking the engine—not ideal.


Public Health Ontario and the Public Health Agency of Canada (PHAC) recommend that sexually active people, particularly those with multiple partners, should get screened regularly. The recommended frequency varies depending on risk factors, but common guidelines include:

  • Once a year for sexually active individuals.

  • Every 3 to 6 months for those with multiple partners or higher-risk behaviors.

  • During prenatal visits for pregnant individuals, to prevent transmission to newborns.


Common screening tests include:

  • Rapid at-home tests (like those provided in trusti’s kits!)

  • Urine tests (for chlamydia and gonorrhea)

  • Blood tests (for HIV, syphilis, and hepatitis B)

  • Swabs (for infections like HPV, gonorrhea, and chlamydia)


Diagnostic Testing: When Symptoms Show Up

If you have unusual symptoms like pain during urination, unusual discharge, sores, or itching, diagnostic testing is the next step. Unlike screening, which casts a wide net, diagnostic tests are more targeted—designed to confirm or rule out a specific infection.


Let’s say you’re experiencing burning during urination. This could be caused by chlamydia, gonorrhea, or even a urinary tract infection (UTI). A diagnostic test helps determine which culprit is responsible so the right treatment can be given.


Some STIs require specific diagnostic tests, including:

  • Genital herpes: Swab test from an active sore (since herpes blood tests can sometimes be inconclusive for a current infection).

  • Syphilis: Blood tests to detect antibodies.

  • Trichomoniasis: Swab test or urine test.


What If I’m Not Sure Which One I Need?

If you’re not experiencing symptoms but are sexually active, a screening test is your best bet. If you have symptoms or know you were exposed to an STI, go for diagnostic testing. If you're still unsure, talk to a healthcare provider—if anyone knows what to do, it’s them.


The Takeaway

Regular STI testing, whether through screening or diagnostics, is one of the best ways to take control of your sexual health. Screenings help catch silent infections before they cause problems, while diagnostic tests ensure that symptoms are properly addressed.


Remember: STIs don’t always come with flashing warning signs, and taking a proactive approach to testing can save you from bigger issues down the road. So, whether it’s time for your routine check-up or you’re experiencing something unusual, don’t hesitate to get tested!


And hey, if you need a good excuse to skip an awkward family gathering, just tell them you have an "important screening appointment." They don’t need to know what kind!

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