Each infection has a window period, the time after exposure before a test can detect it. In Ontario, the fourth-generation HIV test used by Public Health Ontario detects most infections by 2 to 4 weeks and is considered conclusive at 6 weeks; chlamydia and gonorrhea tests are reliable from about 2 weeks; syphilis from 6 weeks with a repeat at 12; hepatitis B and C from about 6 to 8 weeks. Your provider chooses the timing and any repeat. Tests ordered on a requisition are OHIP-covered and can be collected at any Bio-Test centre without an appointment.
What a window period is
After exposure, an infection needs time to reach detectable levels: either the organism itself, its genetic material, or the antibodies your body makes against it. Testing too early can give a negative result even though infection is present. That is why timing, and sometimes a repeat test, matters more than the test itself. If you may have been exposed to HIV in the last 72 hours, go to an emergency department or sexual health clinic immediately to ask about post-exposure prophylaxis (PEP); do not wait for a test.
Typical window periods used in Ontario
- HIV (fourth-generation antigen/antibody test): most infections detectable at 2 to 4 weeks; considered conclusive at 6 weeks. Some guidance still advises a final test at 12 weeks after a high-risk exposure.
- Chlamydia and gonorrhea (urine or swab NAAT): reliable from about 2 weeks; test earlier only if symptoms appear.
- Syphilis (blood test): from about 6 weeks; repeat at 12 weeks after a significant exposure, as antibodies can take up to 3 months.
- Hepatitis B (blood test): surface antigen from about 6 weeks; some tests at 8 to 12 weeks.
- Hepatitis C (antibody blood test): 8 to 9 weeks for most, up to 6 months in some people; an RNA test can detect it earlier when needed.
- Herpes: swab of a sore at the time; blood antibody tests are not routinely recommended for screening.
These are general figures. Your provider sets the schedule for your situation, including any PEP or PrEP you are taking, which can change timing.
Which samples are needed
HIV, syphilis and hepatitis are blood tests. Chlamydia and gonorrhea use a first-catch urine sample or a swab, depending on the site of exposure; Bio-Test collects both. Our STI testing guide covers confidentiality and how requisitions work, and the urine collection guide explains a first-catch sample.
When to retest
A negative result inside the window period is reassuring but not final. Your provider will usually ask for a repeat at the end of the window, and again later for syphilis or hepatitis C after a high-risk exposure. Keep any repeat appointments even if you feel well; most STIs cause no symptoms.
Where to get tested in Ottawa
With a requisition from a physician, nurse practitioner, walk-in clinic or sexual health clinic, walk in to any of Bio-Test's 11 centres with your Ontario health card; no appointment is needed and staff never discuss results at the desk. Results go to the ordering provider within 24 to 48 hours for most tests and appear in the patient portal. Ottawa Public Health's sexual health clinic also offers free, confidential testing without a health card.
Coverage
STI tests ordered by an authorized provider are insured by OHIP with a valid health card. If you have no card, Ottawa Public Health can test you at no charge. See what OHIP covers.