Q and A

Question

How long after any risk does it take HIV tests to be accurate?

13 December 2020. Related: All topics, HIV testing.

Hi, I am worried about a recent risk and I want to know how long I have to wait before taking a test. Thanks.

Answer

Answer: Simon Collins

Hi

Thanks for your question as a few people have asked this recently.

i-Base don’t usually answer questions about testing because the service is for mainly about HIV treatment. Also because we have put all the testing info online. (See: https://i-base.info/qa/11844).

However, as this is a technical question and because guidelines recently changed it is good to briefly answer here. The answer also depends on the test you are using.

  1. If you are testing at home and getting the results without posting samples back to a laboratory, these are likely to be ‘3rd generation’ tests. The window period for accuracy is 90 days after the exposure.
  2. If you are sampling at home and posting the sample back to a lab, these ‘3rd generation’ tests have a window of 60 days.
  3. If you want a faster test result you need to go to a sexual health clinic for a ‘4th generation’ test. 4th generation tests will pick up 95% of infections by about 30 days and more than 99% of infections by 45 days.

New UK guidelines (BHIVA) recommend people now wait 45 days instead of the previously recommended 30 days (see page 19 of the PDF referenced below). [1]

This change is to cover public health benefits relating to whether or not a second confirmatory test is needed. The 30-day window meant that a negative result needed to be confirmed a few months later with a second test. The higher accuracy from waiting until six weeks (45 days) means that a second confirmatory test is no longer needed,

However, some people are either extremely anxious about waiting, especially after a higher risk. In this case someone might benefit from an earlier test, even if slightly less conclusive, and then have the confirmatory test later.

It is unclear whether HIV clinics in the UK will still offer this flexibility to test twice when anxiety is high.

Reference

  1. BHIVA/BASHH HIV testing guidelines (2020). See page 19 for test windows)
    https://www.bhiva.org/HIV-testing-guidelines (webpage)
    https://www.bhiva.org/file/5f68c0dd7aefb/HIV-testing-guidelines-2020.pdf (PDF file)