Q and A


Why do I need to repeat a 28-day negative HIV test at three months?

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.


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:

  1. 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.
  2. 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. 


  1. Lisa Thorley

    Hi Rigobert,

    Just because your partner is positive doesn’t mean that you’re going to be positive. If you haven’t already tested then you will need to do this.

    If the man who you had sex with is on medication and his viral load is undetectable, the risk is close to zero. Please see here for more info:


    In response to your questions, yes there are ARV’s that can control HIV. And its definitely possible to live a long life with them.

  2. Rigobert

    I have meet some and made an anal sex, then after one month I realised that my partner is positive. My question is, can I have some medicine to take out my illness? Second, I live for 20 years with HIV?

  3. Lisa Thorley
  4. Hey

    I received a oral sex , after 5 and half months only 20 days to complete 6 months I tested for HIV the doctor said the test I will do detects the HIV virus within 28 days it was blood test and it was for all sexual diseases, the test came out negative , im an athlete too, but after that I had anxiety from the reading online I had tightness in forearm and felt pressure in head and neck also night sweats but the night sweats disappeared after 2 days, retured yesterday I think maybe cause of stress, so testing after 5 months and half is it conclusive ? Do I move on?

  5. Lisa Thorley
  6. sammani

    How accurate is test after 73 days?

  7. Lisa Thorley

    Hi Anthony,

    i-base is a service that is for people who are living with HIV. We do not answer general medical questions from people who aren’t positive.


    i had sex with a lady two week after i begun to have flu and sore throat with dry cough and rash for two to three i went for hiv test three and it was negative including the lady for six month i was still negative.but i sometime got sore throat. what wrong with me.

  9. Lisa Thorley
  10. Talita

    Are HIV tests accurate after four weeks exposure?