An STD test result reflects your status only up to the point of your last possible exposure, minus the window period before infections become detectable. A negative is never permanent: any unprotected sexual contact after your sample was collected can change your status, so results are valid until your next new exposure.
| Item | Days after exposure |
|---|---|
| Chlamydia / gonorrhea (NAAT) | ~14 |
| HIV — NAT | 10–33 |
| HIV — antigen/antibody | 18–45 |
| HIV — rapid antibody | 23–90 |
What "valid" really means for an STD test
A test isn't a vaccine or a lasting certificate. It's a snapshot of what your body showed on the day of the sample, and only for infections that had been around long enough to detect. A new exposure ends a result's usefulness, and so does realizing you tested before an earlier exposure cleared its window period. Many STIs cause no symptoms, so how you feel tells you nothing reliable. Screening is the only way silent infections get caught.
How long are your results good for? Until you have sex with a new or untested partner again. If you and a partner both test, then stay exclusive, that negative holds. The moment a new exposure happens, the clock resets and you're back to thinking about window periods.
How the test actually works
Most testing is quick and undramatic. For chlamydia, gonorrhea, and trichomoniasis, you give a urine sample in a cup or do a self-collected swab, and a lab runs a NAAT (nucleic acid amplification test), which copies and detects the organism's genetic material. For HIV, syphilis, and hepatitis, a clinician draws a small vial of blood. You're in the chair for minutes, and results typically come back in a day or a few.
NAATs are the most sensitive tests available for chlamydia and gonorrhea, which is why guidelines recommend them over older methods. Modern NAATs are highly accurate, with specificity around 99% USPSTF screening guidance. High specificity means a positive is very unlikely to be a false alarm. Sensitivity over time is different: the test can only find what's physically present in the sample, and early in an infection there may not be enough yet.
When to test after exposure: the window period
The window period is the gap between exposure and the point a test can reliably detect the infection. Test inside that gap and you can get a falsely reassuring negative, not because the test failed but because the infection hadn't grown detectable yet. This is the most common reason for a false negative, and it's why a too-early negative should be repeated.
For HIV, the window depends on which test is used. A nucleic acid test (NAT) can detect infection roughly 10 to 33 days after exposure; an antigen/antibody lab test, about 18 to 45 days; and a rapid antibody test, about 23 to 90 days CDC HIV testing. For chlamydia and gonorrhea, a NAAT is generally reliable about two weeks after exposure. If you test sooner because you're worried, retesting later is reasonable when a recent exposure is possible CDC chlamydia guidance.
| Infection / test | Earliest reliable detection after exposure |
|---|---|
| HIV — nucleic acid test (NAT) | About 10–33 days |
| HIV — antigen/antibody lab test | About 18–45 days |
| HIV — rapid antibody test | About 23–90 days |
| Chlamydia & gonorrhea — NAAT | About 2 weeks |
If you're timing a test around a specific encounter, our breakdown of when to test after exposure walks through each infection's timeline so you don't waste a trip testing too soon.
Where to get tested and what it costs
Testing is widely available at doctors' offices, health departments, Planned Parenthood, and Title X family-planning clinics, often free or on an income-based sliding scale. At-home and self-collection kits also exist, which can be a good fit if you'd rather collect a sample privately; just mind the window period so you test at the right time.
You're rarely far from low-cost care. The US has roughly 16,000 federally funded community health centers and about 4,200 Title X family-planning clinics, plus tens of thousands of other public STI clinics, most offering free or sliding-scale visits HRSA health center program. When you're ready to get tested, it helps to know which infections you want covered; you can also compare testing providers if you're choosing between a clinic and an at-home option.
Reading your results and how accurate they are
A negative means nothing was detected in your sample on collection day, which is solid information as long as you were past the window period for every exposure you're worried about. A positive on a NAAT for chlamydia or gonorrhea is reliable thanks to that high specificity, and points to an active infection that needs treatment.
HIV and syphilis work differently, because a single test isn't the final word. Both use a two-step process: an initial screening test, then a different confirmatory test, and the result isn't a diagnosis until the confirmatory step agrees. A reactive rapid HIV test is preliminary and must be confirmed with a follow-up lab test before it counts as a diagnosis. Syphilis testing pairs two different antibody tests for the same reason; if you've seen confusing syphilis numbers, our explainer on the syphilis rpr vs treponemal test explained breaks down why two tests are used and what each one measures CDC syphilis lab recommendations, 2024.
If a result is positive
Most bacterial STIs are cured with a short, standard course of treatment, and a confirmed positive should be treated promptly. See our treatment guidance and don't stop until the regimen is complete and any partners are notified.
When to see a clinician
Reach out to a clinician if any of the following apply, rather than waiting on a result alone:
- You tested before the window period closed and got a negative, which means you need a repeat test at the right time.
- You have symptoms (discharge, burning with urination, sores, pelvic or testicular pain) even if a test was negative, since the timing or sample may have missed an early infection.
- You got a reactive rapid HIV test or a positive screening test that hasn't been confirmed yet.
- You've had a new partner or a condom failure since your last test and want to know your current status.
- A partner tells you they've tested positive, in which case you may need treatment regardless of your own result timing.