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.
So, from what you are saying I would not have to worry anymore? I had sex with a prostitute and the condom broke and I tested negative for HIV at 3 weeks, 6 months and 15 months. Am I safe?
Thanks
Hello,
Firstly I should point out that we are not doctors but HIV treatment advocates.
You cannot get HIV from receiving oral sex or from protected sex. Your tests are all negative. You do not have HIV. Your symptoms are not HIV-related and you should speak to your doctor so that he/she can investigate further what is causing them.
Dear Doctor.
Please please help me. I am 24yrs old. I am from South Africa. My ordeal stared on the 26th October 2010 where I was involved in a one night stand with a lady. I did use protection when penetrating her; however oral was done on me without protection. Our sex only lasted about 15min. Before I came she touched me near my anus with her fingers. This was not during penetration when I came into the condom.
The first two weeks went by and then around the 9 to the 11th Nov 2010 my penis was feeling really strange (like small, no feeling and pulsating sometimes). I was scared to hell that I might have contracted something from this lady which I have not known her and her past at All. I went to the hospital for a HIV test (Type I & II) on the 12th Nov and picked up blood result on the 13th Nov 2010.
It turned out to be non-reactive. This is what was stated exactly on the Pathology report.
THE HIV ANTIGEN/ANTIBODY COMBINATION ASSAY REDUCES THE WINDO PERIOD BUT NO HIV ASSAY COMPLETELY REMOVES THE WINDOW PERIOD.FOR KNOWN RECENT HIV EXPOSURES A FOLLOW UP TEST IN 10-14 DAYS IS RECOMMENDED.
I must admit I did feel a bit better, but I was still feeling not too good. Maybe the guilt is taking over me as I am in a serious relationship. I deeply deeply regret what I have done doctor. Anyway I was still doing a lot of reading on the net regarding the early symptoms of HIV and I was and still am paranoid.
I went to see another doctor and told him the whole situation; he checked my urine all fine and said it must be in my head. He prescribed Cifloc 250 (antibiotic) for my penis feeling strange and some stress tablets. Everyone is noticing I’m not the same person anymore and I’m totally out of it. My throat today is a bit sore and still worried to hell. I’m scared for what I have done to my girlfriend as we did have sex without protection a few days after the incident. I’m scared that if I am positive I don’t know how I will cope and probably do something really stupid to myself. I’m so scared for my girlfriend as well. Its eating me up doc.
I have learnt my lesson doctor, really, I just hope in Gods gracious name I’m ok. Please advise what should I do? I would really appreciate your point of view.
If you use a condom and it did not break then there is no risk. You do not have HIV. You do not need another test.
How big of a risk is there if anyone uses a condom during intercourse and it did not break and they received a blow-job? Is there any need to test after three months if the first test was negative?
No test alone is 100%. HIV tests, as with anything in life, always have very rare anomalies which do not fit the general rule. If you are taking a fourth generation test at 28 days it is over 95% accurate. If you take a second one at 3 months then it is over 99% accurate.
How long after a possible exposure will a test give 100 % accurate result
Hi Bello,
I hope you don’t mind my answering this instead of Simon? I am not sure I remember saying ‘99.89%’ but I am sorry if I gave you the wrong information. The current thinking is that at 28 days it is over 95% accurate but that a second test at 12 weeks, for people who have had a high risk exposure, would make it over 99% accurate. A 28 day test at over 95% accurate is considered conclusive.
As Simon indicated, nothing is ever 100%. It is our understanding that everyone produces p24, but not always at higher enough levels for the sensitiviy of the test. I am sorry we cannot give you a 100% definite answer but HIV is still a relatively new research area and there are still some things that are unknown.
Thanks
Charlie
Simon
Sorry I didnt add this question – surely this is a typo?
“recognising that the vast majority of infections (over 95%) were likely to be detected after four weeks.”
Do you mean before four weeks? 95% after if certainly not conclusive at 28 days.
Bello
Thank you Simon for your detailed reply.
I would like to ask a confirmation question, That on speaking to Charlotte last week the accuaracy % was 99.89% at 28 days and this would grow as time went on when testing with the Duo/combi test undertaken in a GUM NHS clinic within the UK. This was considered as conclusive?
I believe that BASHH would be conserative with there data,
I have done some research into to the P24 antigen and it would seem that this response would always be present in early infection, and thus the test would pick this up well within 28 days. I understand that antibody production may be delayed but not the P24.
Am I correct in this understanding.
Regards
Bello