Question
Why do I need to repeat a 28-day negative HIV test at three months?
16 September 2023. Related: All topics, HIV testing.
I don’t understand how if a 28 day Duo test when negative is conclusive, why does the information on i-Base say …
“As with antibody tests, a small percentage of people may have a delayed response to HIV so people using this test four weeks after any potential exposure are routinely recommended to confirm a negative result three months later.”
I was negative at 35 days and was moving on with my life until I read this,
please help.
Answer
Note: Since 2021, UK guidelines recommend that a negative result at six weeks using a 4th generation HIV Ag/Ab test does NOT need to be confirmed with a second test. Testing earlier than 6 weeks still needs a second test to confirm a negative result. The earlier answer is kept online to explain the complications of HIV teting. See https://i-base.info/qa/11844
……………
UK recommendations have changed several times on this question. In 2010 when this question was first posted, UK guidelines routinely recommended retesting so the i-Base information referenced this.
Since 2014, the guidelines change to only recommend retesting if this was linked to a high risk of HIV. (See statement below).
Updated guidelines also recommend not having to wait for 28 days before testing. Instead, it is better to test as soon as possible and then retest 4 weeks later. This change was important. It stops people worrying and might pick up early infections. Unfortunately, we still hear of clinics ask people to wait 4 weeks (or longer) before testing.
Even with tests that are incredibly accurate, health care workers have a duty to explain the best chance for a confirmed negative status. The reason for recommending the confirmatory test is two-fold:
- A small number of people have individual responses to HIV that may not be picked up by the test at 28 days. When the tests are approved, this is based on a panel of responses from an extensive store of timed blood samples. These show that some samples pick up a positive test result after only a week and some after more than a month, but that most are positive for the p-24 antigen at around 15 days. Some people may not produce enough p-24 antigen for the test to pick this up though, so together with the antibody response, the combined test are still more than 95% accurate at four weeks.
- The second reason relates to the possibility that someone who is not picked up, might put another person at risk of HIV. This duty of care should be explained when you take the test the test and are given the results. So although you have almost certainly not caught HIV, you should use condoms with sexual partners, until the confirmatory result.
I wish there was an accurate test at two weeks or one day, but there isn’t. The technology is more complicated than most people realise, and the concern for future transmission of HIV, however slight the possibility, is a professional health care concern.
Please don’t let this cause you stress, you are almost certainly HIV-negative, but this is the detailed reason.
BASHH/EAGA Statement on HIV window period
November 2014
HIV testing using the latest (fourth generation) tests is recommended in the BHIVA / BASHH / BIS UK guidelines for HIV testing (2008). These test for HIV antibodies and p24 antigen simultaneously. A fourth generation HIV test on a venous blood sample performed in a laboratory will detect the great majority of individuals who have been infected with HIV at 4 weeks after specific exposure.
Patients attending for HIV testing who identify a specific risk occurring less than 4 weeks previously should not be made to wait before HIV testing as doing so may miss an opportunity to diagnose HIV infection (and in particular acute HIV infection during which a person is highly infectious). They should be offered a fourth generation laboratory HIV test and be advised to repeat it when 4 weeks have elapsed from the time of the last exposure.
A negative result on a fourth generation test performed at 4 weeks post-exposure is highly likely to exclude HIV infection. A further test at 8 weeks post-exposure need only be considered following an event assessed as carrying a high risk of infection.
Patients at ongoing risk of HIV infection should be advised to retest at regular intervals.
Patients should be advised to have tests for other sexually transmitted infections in line with advice on window periods for those infections (see BASHH guidelines at: www.bashh.org ).
Note: This answer was updated in January 2018 from an original post from October 2010. The additional note was added in September 2023.
If you have a question about catching HIV, risks or testing please read this FAQ page on HIV transmission and testing. It will answer most questions.
https://i-base.info/qa/factsheets/hiv-transmission-and-testing
A new Guide to sexual transmission and HIV testing contains more detailed information, including on oral sex.
http://i-base.info/guides/testing
Please read this resource. It will also answer your questions.
I do unprotected oral sex 2 month ago I tested hiv after 2 month after exposure. I get hiv non reactive result. is this result accurate ? Or how much accurate ?
see: http://i-base.info/guides/testing
Hi doctor, i had an unprotected sex for only 2 minutes at the last moment. But i afterward felt its really dangerous. I didnt cum as well. Will i be the victim of HiV positive? On the same day, i went to doctor and had blood test. The result was negative. The lady is someone who I pad to have sex.
http://i-base.info/guides/testing
This is the fourth week, a month. I took a test today for HIV and the following stds and tested neg for HIV meanwhile I wait an additional week for the remaining test. I was just wondering if I should go back at 3 month then 6 for another test ? Please help.
I’m sorry but i-Base no longer answers individual questions about risks of HIV transmission or HIV testing.
This service is based on information relating to treatment of people who are HIV positive.
Information online
Most testing questions are already answered on the FAQ page:
https://i-base.info/qa/faq/hiv-transmission-and-testing
Our guide to HIV Testing and risks of sexual transmission guide has more detailed and easy to read information about these topics. It can be read online at this link:
http://i-base.info/guides/testing
Worried about HIV?
If you are worried about a possible infection contact your local testing centre.
In the UK you can find your nearest clinic using the NHS website:
http://www.nhs.uk/ServiceDirectories/Pages/ServiceSearchAdditional.aspx?ServiceType=SexualHealthService
Understanding HIV test results:
If you do not understand results from an HIV test, please contact the centre where you were tested.
Worried about symptoms?
If you are concerned about any symptoms please contact a doctor.
I had sex and my condom broke and 3 days later I noticed that I had itching on my penis. I told her to go get checked and she did HIV blood test and a swab test, she came out negative on HIV but she had an std called Trichomonas.
My questions are
I did HIV blood test 1month after possible exposure and came out Negative! how accurate is it?
Thanks
I’m sorry but i-Base no longer answers individual questions about risks of HIV transmission or HIV testing.
This service is based on information relating to treatment of people who are HIV positive.
Information online
Most testing questions are already answered on the FAQ page:
https://i-base.info/qa/faq/hiv-transmission-and-testing
Our guide to HIV Testing and risks of sexual transmission guide has more detailed and easy to read information about these topics. It can be read online at this link:
http://i-base.info/guides/testing
Worried about HIV?
If you are worried about a possible infection contact your local testing centre.
In the UK you can find your nearest clinic using the NHS website:
http://www.nhs.uk/ServiceDirectories/Pages/ServiceSearchAdditional.aspx?ServiceType=SexualHealthService
Understanding HIV test results:
If you do not understand results from an HIV test, please contact the centre where you were tested.
Worried about symptoms?
If you are concerned about any symptoms please contact a doctor.
I tested negative for HIV 42 days after unprotected sex,but i was diagnose with gonnerrea ,but I got treated and its gone,do I have HIV+