The window period is the time between an infection and the moment a test can reliably detect it. During that window there is too little bacterial material, virus or antibody present to measure. A negative result within the window period therefore does not rule out an STI.
How long to wait depends on the STI and the test method. Bacterial STIs such as chlamydia and gonorrhoea are detectable fairly quickly with a sensitive PCR (NAAT), whereas antibody blood tests — as for syphilis, HIV and hepatitis — need longer. The guidance per STI is below.
Chlamydia and gonorrhoea: from about 2 weeks
The NAAT (PCR) on urine or a swab is usually reliable from about two weeks after the risk contact. For certainty the GP guideline (NHG) uses three weeks; if you test earlier and the result is negative, a repeat test is advised. After oral or anal sex, remember a throat and anal swab, because a urine test misses those infections.
Syphilis: from about 6 weeks
Syphilis is detected with a blood test (serology), usually reliable from about six weeks after the risk contact. In the very early primary stage the result can still be negative, so if there is any doubt a repeat test follows after three months. If there is already a fresh ulcer, a clinician can test material from it directly (PCR) — often before the blood test turns positive.
HIV: from 6 weeks to 3 months
A modern lab HIV blood test (fourth generation, measuring both antibodies and the p24 antigen) is reliable from six weeks. A negative result after six weeks is reassuring, but for full certainty many guidelines use three months. Rapid tests and self-tests based on antibodies alone (finger-prick) have a longer window period of up to three months.
Hepatitis B and C
Hepatitis B and C are found with a blood test. Hepatitis B is usually detectable from about six weeks to three months; for full certainty a check at six months is sometimes done. For hepatitis C the window period can run to several months. If you are not vaccinated against hepatitis B and are at risk, discuss vaccination as well.
Do you have symptoms? Then do not wait
The window period applies to testing without symptoms. If you do have symptoms — discharge, pain when urinating, a sore, a rash or fever — get checked straight away, even within the window period. With symptoms a clinician can often test more specifically (for example a culture or a PCR of a sore) and start treatment sooner if needed.
Recent HIV risk? Consider PEP within 72 hours
If there has been a high HIV risk — for example unprotected sex with someone who is HIV-positive and not on treatment — PEP (post-exposure prophylaxis) can still prevent an infection. PEP must be started as soon as possible and no later than 72 hours after the risk. Call the GGD, the out-of-hours GP service or the emergency department right away; waiting for a test result is not an option here.
Tested too early? Repeat the test
Did you test within the window period and get a negative result while there was a real risk? Then repeat the test after the recommended period. And remember: a test only says something about infections from before the window period. If there was another risk contact after your test, a new test is needed. Unsure which test and which sampling sites fit your situation? Use our decision helper.
This information is general and was compiled with care from public sources, but it does not replace medical advice. For symptoms or doubt, always consult a doctor.
