When to test after exposure
Every STI has a “window period” — the gap between exposure and when a test can reliably detect infection. Testing too early can miss an active infection. The right window depends on the infection, the test technology, and clinical context. Below are typical timelines from CDC guidance and FDA test labeling, plus when most clinicians recommend retesting. Talk to a clinician about what’s appropriate for your specific situation.
Short answer
- Chlamydia & gonorrhea (NAAT): often detectable within ~5–7 days; many clinicians retest at 2 weeks if the initial test is negative and exposure is recent.
- HIV (4th-gen Ag/Ab): typically detectable around 18–45 days; the FDA-cleared 4th-gen tests are generally considered conclusive by ~45 days post-exposure.
- Syphilis: typically detectable by 3–6 weeks via treponemal/non-treponemal testing.
- Hepatitis B & C: typically detectable by 3–6 weeks (HBsAg) and up to 8–11 weeks for HCV antibody.
- If you had a high-risk exposure within 72 hours, talk to a clinician about HIV PEP and/or doxy-PEP — the prevention windows are short.
Detection windows at a glance
| Infection | Test | Typical window | Often considered conclusive |
|---|---|---|---|
| Chlamydia | NAAT (urine/swab) | ~5–7 days | ~2 weeks |
| Gonorrhea | NAAT (urine/swab) | ~5–7 days | ~2 weeks |
| HIV | 4th-gen Ag/Ab (lab) | ~18–45 days | ~45 days |
| HIV | 3rd-gen Ab (rapid finger-prick) | ~23–90 days | ~90 days |
| HIV | NAAT (RNA, viral load) | ~10–33 days | ~33 days; used for early detection |
| Syphilis | Treponemal + non-treponemal | ~3–6 weeks | ~12 weeks |
| Hepatitis B | HBsAg | ~3–6 weeks | ~9 weeks |
| Hepatitis C | Anti-HCV antibody | ~4–11 weeks | ~6 months |
| Trichomoniasis | NAAT | ~5–28 days | ~4 weeks |
Windows compiled from CDC STI Treatment Guidelines, CDC HIV testing recommendations, and FDA test labeling. Individual test brands may have slightly different detection windows — check the test’s package insert if exact timing matters.
Practical scheduling
- Within 72 hours of high-risk exposure: talk to a clinician about HIV PEP (28-day course) and/or doxy-PEP (single 200 mg dose). PEP windows are short and the medications are most effective when started ASAP.
- ~1–2 weeks post-exposure: chlamydia and gonorrhea NAAT becomes reliable. Reasonable time for an initial cash-pay or insurance-covered test.
- ~4–6 weeks post-exposure: 4th-gen HIV testing becomes broadly reliable. Syphilis and HBV usually detectable.
- ~3 months post-exposure: a follow-up panel is often recommended to catch later-window infections (HCV antibody, late seroconversion).
- If treated for chlamydia or gonorrhea: CDC recommends rescreening at 3 months because reinfection from untreated partners is common.
If you have symptoms
Don’t wait for a window period. Symptoms (discharge, sores, painful urination, pelvic pain, rash) mean a clinician evaluation today — testing in a symptomatic context is diagnostic, not screening, and the timing/coding rules are different.
Sources: CDC STI Screening Recommendations · CDC HIV Testing · CDC HIV PEP · CDC STI Treatment Guidelines 2021. Verified May 2, 2026.
This page is a decision aid — general information, not medical advice. See methodology for how we rank options.