How do urine tests detect STIs?

Dear Ani,  

This is a great question! Knowing what you’re being tested for, and how, helps you make more informed decisions about your sexual health. 

Urine tests are primarily used to check for gonorrhea, chlamydia, and occasionally trichomoniasis, since they directly infect the urethra or cervix. Your sample is sent into a machine that checks for any of the infections’ DNA hiding in your urine. Although urine tests are generally reliable, they can be less accurate for people assigned female at birth (AFAB). Therefore, vaginal swabs are becoming a more popular method to test for STIs in people AFAB.  

What STIs can urine tests detect?  

Urine tests are most commonly used to detect gonorrhea, chlamydia, and sometimes trichomoniasis. There’s a urine test for Human Immunodeficiency Virus (HIV), but it’s rarely used, so blood tests are the go-to for HIV. Other infections—including herpes, syphilis, and hepatitis B—can only be picked up with blood tests. 

How is urine examined to detect a STI?  

Gonorrhea and chlamydia are caused by bacteria that infect the urethra and the cervix (in people with vaginas). The urethra “sheds” bacteria when urine passes through it, and STI tests work by detecting the presence of the bacteria’s DNA in urine.  

Once your urine sample is collected, it’s run through a machine that replicates the bacterial DNA if it’s present, until there’s enough to be detected. This method allows even tiny amounts of DNA to be recognized. 

How accurate are urine tests for STIs?  

In general, urine tests for STIs are quite accurate. You'll get the greatest accuracy by using “first-catch” urine for your sample, since your first pee of the day to pass through the urethra will likely have the greatest number of bacteria. You might be asked not to clean your genital area before taking the test, since cleaning can reduce the number of bacteria in your urine.   

Urine tests tend to have a greater accuracy for people assigned male at birth (AMAB) than for people assigned female at birth (AFAB). In AMAB people—including those with a surgically-constructed vagina—the bacteria usually set up shop in the urethra, right along urine’s main highway. It’s more common for bacteria to infect the cervix than the urethra in AFAB people. Since urine doesn’t come in contact with the cervix, these tests can only detect infection if a little cervical or vaginal fluid tags along at the very start of urination. That’s why it’s recommended for AFAB people specifically to take a “first-catch” sample for an STI test. Alternatively, a provider may recommend a swab. 

If you're interested, you can consider asking a health care provider if they offer vaginal swab testing as an alternative to urine tests. However, even if that option isn’t available, urine tests are still a relatively accurate way to detect STIs.  

Here's to putting your best test forward!