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Do I Need a Blood Test to Detect STIs?

  • Writer: Trusti Team
    Trusti Team
  • Apr 2
  • 4 min read

Updated: Apr 4

Getting tested for sexually transmitted infections (STIs) is one of the most responsible things you can do for your health and the health of your partners. But with all the different types of tests out there—urine tests, swabs, and yes, blood tests—it’s natural to wonder if you need to roll up your sleeve every time you get checked.


A blood test isn't always necessary, so let's dive into when you need one and when you don't, and how to prepare for one if you do need it.


Not All STIs Require a Blood Test

Many common STIs can be detected without a blood test. For bacterial infections like chlamydia and gonorrhea, a urine test or swab is typically all that’s needed. These tests check for bacteria in the urine or from a sample taken from the affected area (like the cervix, throat, or rectum). According to the CDC, these infections are among the most commonly reported in the U.S., and PHAC notes that chlamydia is the leading bacterial STI in Canada. Thankfully, testing for them is simple, painless, and doesn’t involve a needle.


Other STIs, like trichomoniasis, are usually diagnosed with a swab or urine test as well. If your main concern is one of these infections, you can breathe easy—no bloodwork required.


When a Blood Test Is Necessary

While many STIs can be detected through urine or swab tests, some require a blood test for accurate diagnosis. These include:

  • HIV: A blood test (full blood draw or rapid finger-prick) is the most reliable way to detect HIV. The CDC recommends routine testing for everyone aged 13-64, especially those with multiple partners or other risk factors. The earlier HIV is detected, the better the treatment outcomes, so regular testing is a key part of staying healthy.

  • Syphilis: This STI is on the rise in both the U.S. and Canada, according to data from the CDC and PHAC. While the first symptom of syphilis is often a painless sore (called a chancre), a blood test is needed to confirm the infection.

  • Herpes (HSV-1 & HSV-2): While herpes can sometimes be diagnosed based on visible sores, a blood test may be used if symptoms aren’t present but exposure is suspected. The test looks for antibodies to the virus, though it doesn’t always indicate when or how the infection was acquired.

  • Hepatitis B and C: Hepatitis B and C are viral infections that affect the liver and can be transmitted sexually. Both can be detected through blood tests, and PHAC strongly recommends hepatitis B vaccination for those at risk.


Full Blood Draw vs. Rapid Testing

Diagnostic technologies are innovating at an impressive rate. You can now get results for conditions like HIV and syphilis in as little as 60 seconds today. You may be wondering what the difference is between a rapid finger-prick blood test versus a full blood draw – because, let’s be honest, who likes watching their blood getting taken?

  • Full Blood Draw:

    • Full blood draw tests are when a health practitioner uses a sterile needle to pierce a vein and withdraw blood into vials. While it can be an uncomfortable process, it is crucial for screening for some STIs.

    • A full blood draw test for a viral infection, like HIV, is particular useful for it’s ability to detect infection early typically within 10-18 days, and for detecting viral load.

  • Rapid Finger-Prick Blood Test:

    • There are a few rapid tests that require a finger-prick blood sample. Currently, there are HIV self tests (like the one including in Trusti’s HIV Testing Kit), and some syphilis/HIV dual rapid tests available in certain settings. The tests require a prick of the finger with a sterile lancet and then a drop of blood in one of the test’s solutions. It’s a similar process to pricking the finger for a blood sugar reading.

    • While HIV rapid tests are convenient, affordable, and provide incredible fast results, they do have some limitations. HIV rapid tests are not best for early detection and do not detect viral load. If you think you may have been exposed to HIV, it’s important to seek in-person care and get a full blood draw sample for these reasons. If you test positive on a rapid HIV test, confirmatory testing with a full blood draw sample is required in order to assess viral load.


How Often Should You Get Tested?

The frequency of STI testing depends on several factors, including your sexual activity and risk level. The CDC and Public Health Ontario recommend:

  • At least once a year for sexually active individuals, especially those with multiple partners.

  • Every 3-6 months for people with higher risk factors, such as those in non-monogamous relationships, men who have sex with men, or those with a previous STI diagnosis.

  • Routine testing during pregnancy, as some infections can be passed to the baby.


Takeaway: Blood Test or Not, Just Get Tested

While not all STIs require a blood test, the most important thing is to get tested regularly and stay informed. Whether it’s a simple urine test or a quick blood draw, STI testing is a normal and essential part of sexual health. And remember, taking control of your health isn’t just responsible—it’s empowering.


So if you’re due for an STI test, don’t put it off. Whether it’s a blood test, swab, or urine sample, knowing your status is the best way to protect yourself and your partners. And hey, if you get a cool bandage out of it, consider it a tiny badge of honour for being proactive about your health.


Want to do an STI test from home? Subscribe to Trusti’s newsletter to find out when tests for these conditions are available in your location.

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