When to Retest After STI Exposure — by Infection

You had a possible STI exposure. You got tested. The first test was negative. Are you in the clear?

Maybe not — depending on which STI and how long after exposure you tested. Each STI has its own window period (when the test first turns positive) and a separate retest interval to be sure.

Here's the exact schedule.

The short answer (retest timing)

Why retesting matters

Tests detect different markers at different speeds:

1. PCR/NAAT tests detect the pathogen directly — fast (days to weeks)
2. Antigen tests detect part of the pathogen — fast for some, slow for others
3. Antibody tests detect your immune response — slower (weeks to months)

The "window period" is the gap between exposure and when the test reliably turns positive. Testing during the window can give false negatives. A negative test at week 1 doesn't mean you're clear.

STI by STI

HIV

4th generation antigen/antibody test (most common)

• First positive: 18-45 days after exposure
• Conclusive negative: 45 days for ~95% of people; 3 months for everyone
• Retest: If first test < 45 days post-exposure, retest at 6 weeks. If high-risk exposure, retest at 3 months.

RNA / NAAT test

• Detects viral RNA directly. Most sensitive early.
• First positive: 10-14 days
• Conclusive negative: 28-30 days
• Retest: If concerned about earlier exposure, retest at 4-6 weeks
• More expensive; usually only for occupational exposure, PEP follow-up, or symptomatic HIV concern

Oral rapid antibody test (OraQuick)

• Less sensitive in the first 3 months
• Conclusive negative: 3 months
• Retest: at 3 months if exposure recent

PEP completion follow-up

If you took HIV PEP (post-exposure prophylaxis):

• Baseline HIV test
• HIV test at 4-6 weeks after starting PEP
• HIV test at 3 months after starting PEP

Chlamydia

• NAAT: detects DNA. Sensitive within 1-2 weeks.
• First test: 7-14 days after exposure
• Retest if negative and concerned: 2-3 weeks
• After treatment: Test of cure NOT routinely needed for chlamydia. Retest at 3 months to catch reinfection (very common).

Gonorrhea

• NAAT: sensitive within 5-7 days
• First test: 5-14 days after exposure
• Retest if negative and concerned: 2 weeks
• After treatment:
  • Urogenital gonorrhea: no test of cure
  • Pharyngeal gonorrhea: test of cure at 7-14 days after treatment (throat is hardest to clear)
  • Retest at 3 months for all sites to catch reinfection

Syphilis

• First positive: 3-6 weeks (chancre typically present at ~3 weeks)
• Conclusive negative: 3 months
• Retest if early test negative and concerned: at 6 weeks and 3 months
• After treatment:
  • Repeat RPR at 6 and 12 months
  • For late latent syphilis: also at 24 months
  • Expected fourfold drop in RPR titer (e.g., 1:32 → 1:8)
  • Treponemal test stays positive for life
• See syphilis testing process for details

Hepatitis B

• HBsAg (acute infection): turns positive 1-9 weeks; peaks at 3-6 weeks
• HBcIgM (recent infection): 4-8 weeks
• Retest if negative and exposure recent: 6 weeks, 3 months, and 6 months
• If exposed and not immune: consider HBIG + vaccine within 24 hours, complete series
• Long-term follow-up: at 6 months to confirm cleared vs chronic

Hepatitis C

• HCV antibody: 8-11 weeks typical, can take up to 6 months
• HCV RNA (PCR): 1-2 weeks
• First test: 8-11 weeks; HCV RNA earlier if urgent
• Retest: at 12 weeks and 6 months if exposure suspected
• If positive antibody: PCR to confirm active infection (some clear spontaneously)

Herpes (HSV)

PCR swab (active lesion present)

• Definitive if positive
• No retest needed if you have a clear lesion-based diagnosis

IgG blood test (no active lesion)

• First positive: 3-6 weeks after first infection
• Conclusive: 16 weeks after exposure
• Retest if first test negative and concerned: at 12 weeks and 16 weeks
• See herpes blood test accuracy — false-positive issues with low-positive results

HPV

• No general clearance test for asymptomatic HPV in the genital area (men) or oral area
• In women: Pap smear / HPV co-testing schedule per age and prior history (every 3-5 years)
• For new symptoms: clinical evaluation, biopsy if needed
• Anal Pap / HRA for high-risk individuals

Trichomoniasis

• NAAT: sensitive within 3-7 days
• First test: 5-14 days
• Retest if negative and concerned: 2 weeks
• After treatment: Repeat NAAT at 3 months — reinfection common

After-treatment retesting summary

After being treated for any STI, the "did the treatment work?" question matters:

Specific scenarios

"I tested 3 days after exposure and it was negative"

For HIV, chlamydia, gonorrhea — too early. Repeat per schedule above.

"I tested at 4 weeks for HIV and it was negative"

For 4th gen HIV test: ~95% conclusive. Repeat at 6 weeks for full confidence.

"I had unprotected sex 6 months ago — am I clear if my tests are negative now?"

Yes for HIV, chlamydia, gonorrhea, syphilis (single exposure). HPV doesn't have a clearance test.

"I'm on PEP — when do I test?"

At 4-6 weeks and 3 months after starting PEP. Continue safer sex during this period.

"I had sex with someone who later disclosed they have herpes"

• If you develop symptoms: PCR swab the lesion (definitive)
• If no symptoms: HSV IgG blood test at 12 and 16 weeks
• Discuss with provider about validity of testing given low-positive issues

"I was just treated for chlamydia — when can I have sex again?"

7 days after treatment AND after partner(s) are treated. Retest at 3 months for reinfection.

See sex after STI treatment for full schedule.

What if a retest is positive after a negative test?

This can mean:

• The initial test was within the window period and missed it
• You had a new exposure between tests
• The test had a false negative (uncommon with modern testing)
• Cross-reactivity or technical issue (more common for HSV IgG and syphilis)

The right move: trust the positive result, work with your provider to confirm and treat. Don't dismiss positive results because earlier tests were negative.

Things that can affect window periods

• Immunocompromise (HIV, chemotherapy, transplant) → antibody tests may take longer to turn positive
• Recent treatment for the same or different infection
• Test type and lab quality
• Site of infection (e.g., gonorrhea NAAT from urine is less sensitive than from anatomic site of infection)

Practical advice

1. Get a full panel after any concerning exposure — don't just test for what you think you might have
2. Use the right test for the right site — urine NAAT misses rectal/throat infections
3. Retest per schedule even if first results are negative
4. Use the same lab when possible — easier to compare over time
5. Talk to your provider about your specific exposure timing

Bottom line

A negative STI test isn't always the end of the story. Each infection has a window period and an appropriate retest schedule:

• HIV: retest at 6 weeks and 3 months
• Chlamydia / Gonorrhea: initial test at 1-2 weeks; retest at 3 months for reinfection
• Syphilis: retest at 6 weeks and 3 months
• Hepatitis B: retest at 3 and 6 months
• Hepatitis C: retest at 12 weeks and 6 months
• HSV (blood): retest at 12 and 16 weeks
• Trichomoniasis: retest at 2-3 weeks

Mark your calendar. Follow through. The cost of incomplete screening is the cost of unknown infection.

For initial-window-period details, see STI testing window periods. For where to test: free STI testing. For after a known exposure: condom broke 72-hour action plan.