When is the best time to go for a HIV screening after sexual contact?

Doctor's Answers 2

Photo of Dr Anthony Stanislaus
Dr Anthony Stanislaus

General Practitioner

Human immunodeficiency virus (HIV) is a form of retrovirus that causes HIV infection. Over time it leads to acquired immunodeficiency syndrome (AIDS).

AIDS is a condition where due to progressive failure of the immune system, allows life-threatening infections which don’t usually bother a healthy person and cancers to thrive in the body. This is why HIV is one of the infections we humans are most worried about after a sexual encounter.

There are a few ways to detect HIV in the blood and each method has different testing window periods.

Window period is basically the time between potential exposure to HIV infection and the point when the blood test will give an accurate result.

The most commonly ordered tests in Singapore for detecting HIV are:

  • HIV antibody test (3rd generation)
  • HIV antigen/antibody test (4th generation).

The HIV antigen, also known as p24, may become detectable in the blood 14 to 20 days after an infection and peaks at about day 30.

On the other hand, the HIV antibodies may become detectable as early as day 20 to 23 but in some cases, it may take longer.

With this in mind, the earliest you can undergo a HIV antigen/antibody (4th gen) test is 2 weeks after an exposure but a repeat test will need to be done at the 4-week mark where the p24 is at its peak and the test is deemed accurate.

The HIV antibody test (3rd generation) test is best performed at the 3-month mark for it to be deemed conclusive.

With these in mind, there are in fact other tests which may be able to detect HIV before the 4 week mark, however, it is very costly and the waiting time to get the results are long and therefore are not usually recommended.

It is therefore best to see a doctor with experience in HIV testing who will be able to tailor the tests to your history. Do note that there are rapid tests available in some clinics in Singapore, that will be able to give you a result in 30 minutes.

The best way to determine a HIV infection is to have a screening after the window period, which is between 1 to 3 months after an exposure.

It is advisable to go for a HIV test at month 1, and to repeat the test at month 3 to obtain a conclusive result.

Most people with HIV do not show any signs and symptoms. However, some may have a flu-like illness with:

  • Swollen lymph nodes
  • Fever
  • Discomfort
  • Rash lasting about 2 – 3 weeks soon after acquiring HIV.

Very often, people do not have signs and symptoms for several years.

The advanced stage of HIV can take an average of 8 to 10 years from the time of being infected for an untreated person.

Symptoms like fever, unexplained weight loss and diarrhoea are common. Rare cancers and infections may develop, and common infections may be severe.

Early detection will assist in the management of this infection in terms of treatment, transmission and lifespan.

Similar Questions

Do I still need to go for HIV screening if my STD screening test is non-reactive?

Dr Theng has given a wonderful answer. Oral sex is generally considered safe but there is a low risk of transmission if there are some open wounds which may not be obvious.

Photo of Dr Winston  Lee

Answered By

Dr Winston Lee


Can HIV tests be considered conclusive if they show negative results?

Thank you for the question. For HIV test, there is a window period, which is the period between the time of exposure to the time the test is able to detect the infection. For 4th generation HIV test, the window peroid is 4 weeks and for 3rd generation HIV test, it is 3 months. So with your 2 tests at 1 and 3 months negative, it is highly unlikely that you have caught an HIV infection. In recent HIV infection, the presentation can be very non specific, like any viral infection. However, years later, it can present with recurrent infections or unusual infections due to reduced immunity.

Photo of Dr Colin Theng

Answered By

Dr Colin Theng


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