Why You Might Not Realize You Have an STI Even After Testing

Testing for sexually transmitted infections (STIs) is one of the best things you can do to protect yourself and your partner(s) from disease. However, STI tests aren't perfect. It is possible to get a negative test result and still have an STI.

Given the potential impact of some STIs—from genital warts to fertility issues to cancer and more—it may seem unlikely that you could have one and not know it. But very often, that's the case.

According to an analysis published in the journal Sexually Transmitted Diseases, an estimated 1 in 5 people in the U.S. had a sexually transmitted infection (STI) on any given day in 2018. Some knew about their diagnosis, while some did not.

There are several potential reasons why STI tests aren't infallible.

Couple consulting doctor in his office
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You May Not Have Actually Been Tested

Many people think that their healthcare provider screens them for STIs as part of their annual exam. This, unfortunately, may not be true. Some providers don't regularly screen patients for STIs. It's also easy to confuse tests like a Pap smear or pelvic exam for an STI test.

The only way to be certain you're getting tested for STIs is to ask your provider to test you. If you have a known exposure, mention it. Be open about your sexual history (past and present), number of partners, how you have sex, and what (if any) preventive measures you take. All of this can highlight the need for specific tests.

You May Have Been Tested Too Soon

Some STI tests are not effective for a newly acquired infection. For example, a study published in 2014 showed that the standard blood test for syphilis is ineffective at detecting early cases of the disease.

Some STI tests, like HIV tests, look for an antibody response (instead of the sexually-transmitted bacterium or virus itself). Antibodies are specific proteins your immune system produces in response to infection.

These tests may be particularly susceptible to errors when given too soon, as it can take several weeks for an antibody response to develop.

The Test Gave an Inaccurate Result

When designing a diagnostic test, there is always a trade-off between sensitivity and specificity.

Almost no test is going to be perfectly able to determine whether or not someone is infected. The ability of an STI test to predict your health is dependent, in part, on the population that test is being used in.

Most tests are designed to be pretty good, and there are almost always ways to make their results more accurate. Still, both false positives and false negatives can be a problem. Which problem you need to worry about depends on the disease in question and the test that is being used to detect it.

That said, if you recently tested negative for an STI but are still experiencing symptoms, let your healthcare provider know and consider getting tested again. 

Your Healthcare Provider Didn't Test for the STI You Have

Although there are many different tests that can detect STIs, like chlamydia or HIV, there is not one that is able to detect all STIs. Some STI tests need a urine or blood sample, while others may require a genital, rectal, or oral swab.

That said, your healthcare provider may only recommend certain STI testing based on your symptoms, known risk factors, or routine screening recommendations. Depending on your medical and sexual history, they may recommend that you get tested regularly—even if you are asymptomatic.

Keep in mind that these tests cannot detect an infection you might have been exposed to after you were already tested. Therefore, it's important to talk to your healthcare provider about the types of STI testing you may need (based on your risk factors) and how often you should be screened.

4 Sources
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  1. Kreisel K, Spicknall I, Gargano J, et al. Sexually Transmitted Infections Among US Women and Men: Prevalence and Incidence Estimates, 2018Sex Transm Dis. 2021;48(4):208-214. doi:10.1097/olq.0000000000001355

  2. Henao-Martínez AF, Johnson SC. Diagnostic tests for syphilis: New tests and new algorithmsNeurol Clin Pract. 2014;4(2):114–122. doi:10.1212/01.CPJ.0000435752.17621.48

  3. Centers for Disease Control and Prevention. HIV testing.

  4. Workowski KA, Bachmann LH, Chan PA, et al. Sexually transmitted infections treatment guidelines, 2021MMWR Recomm Rep. 2021;70(4):1-187. doi:10.15585/mmwr.rr7004a1

Elizabeth Boskey, PhD

By Elizabeth Boskey, PhD
Elizabeth Boskey, PhD, MPH, CHES, is a social worker, adjunct lecturer, and expert writer in the field of sexually transmitted diseases.