HIV Testing and HIV Window period for early HIV detection in HK

HIV/AIDS Testing

There are three types of HIV tests available: 

  1. nucleic acid tests (NAT),
  2. antigen/antibody tests, and
  3. antibody tests.

HIV testing is usually done in blood or oral fluids. They can also be done on urine.

In 2019, UNAIDS estimated that 7.1 million people worldwide did not know they have been infected with HIV. This could be due to the fact that the symptoms of acute HIV infection are non-specific and not everyone will exhibit signs of infection, therefore, a large number of HIV infection cases remained untested and undiagnosed. If you think you have been exposed to HIV, the only way to know for sure is to get tested. If you suspect that you have been exposed with a high-risk HIV person within 72 hours, you can consider an emergency PEP treatment to prevent HIV infection.

Who should get tested for HIV?

Everyone who is sexually active should get tested for HIV at least once to ascertain their HIV status. However, people at higher risk of HIV infection (high risk groups) should consider getting tested more frequently, including:

  • Gay men or men who have sex with men (MSM)
  • Those who had sex with an HIV-positive partner
  • Those who had new sexual partner(s) since their last HIV test
  • Intravenous drug users, or shared injection equipment with others
  • Sex workers
  • Clients of sex workers
  • Those who were diagnosed with a sexually transmitted disease (STD)
  • Those who had sex with a partner with one or more risk factors listed above

Window period of HIV Tests

The window period refers to the time between HIV infection and when a test can detect HIV infection, which varies between individuals and depends on the target (RNA, antigen or antibody) being detected by the test.
The event of possible HIV exposure (e.g. sex) must took place after the window period of the HIV test in order to get an accurate result. For example, if you had sex 20 days ago, the HIV combo test (window period 14 days) or HIV RNA test (window period 7 days) can be use but not the rapid HIV antibody test (window period 90 days).

HIV TestsWindow Period (Day)
HIV RNA Test7 days
HIV p24 Antigen&Antibody Combo Test14 days
HIV Quick Test90 days

HIV Tests for Early detection

Recent advancement in diagnostic technology have provided newer generations of HIV testing to be performed at higher accuracy with shorter window period. Rapid and reliable diagnosis of HIV infection not only allows the use of anti-retroviral therapy (ART) to be initiated as early as possible, but also plays a crucial role in preventing transmission to others.

(REF: Hurt, C. B., Nelson, J. A., Hightow-Weidman, L. B., & Miller, W. C. (2017). Selecting an HIV test: a narrative review for clinicians and researchers. Sexually transmitted diseases, 44(12), 739.).

There are 3 types of HIV test available:

HIV RNA test

which that detects the the actual number of HIV in the blood. It is also known as is the HIV nucleic acid amplification test (NAAT), or the HIV viral load test. The HIV RNA test is the most sensitive test among all available HIV tests. It can detect the presence and quantity of HIV RNA in venous blood, which is mainly used: 

  1. To confirm suspected HIV infection
  2. To monitor the viral load for HIV-positive people
  3. To detect early HIV infection

Our HIV RNA detection system is an enclosed, fully automatic system and result is available within a few hours. The earliest detection of HIV RNA is about one week post exposure Research suggested that an HIV RNA test with a sensitively of 50 copies/ml would detect HIV infection approximately 7 days before a p24 antigen/antibody test (window period of 14 days). There is currently no research evidence to support the use of HIV RNA test less than 7 days post exposure.

Window period of HIV RNA Test

7 days after exposure

(REF: Stekler J, et. Al., Screening for acute HIV infection: lessons learned. Clinical Infectious Diseases. 2007).
(REF: Fiebig EW, et. Al. Dynamics of HIV viremia and antibody seroconversion in plasma donors: implications for diagnosis and staging of primary HIV infection. AIDS . 2003. 17:1871–1879.)

The HIV RNA Test is not recommended for diagnostic purposes. Some laboratories that perform pooled sample for HIV RNA test with the dilution of samples may result in false-negative test with early HIV infection. Therefore, the result of the 4th generation HIV (p24 combo) test should be used to determine infection status, especially cases with low HIV RNA level.

(REF: Busch MP, et al. Relative sensitivities of licensed nucleic acid amplification tests for detection of viremia in early human immunodeficiency virus and hepatitis C virus infection. Transfusion 2005; 45:1853–63.)

The HIV RNA test is expensive but it has a shortest window period and allows detection of very early HIV infection. You may consider having an HIV RNA test if you had a high-risk exposure, or showing early symptoms of HIV infection after a possible exposure. o An HIV RNA test should not be used to test for HIV infection if you are currently using or recently used post-exposure prophylaxis (PEP), as the medication is known to suppress viral replication which could lead to a false-negative result.

HIV p24 antigen/antibody combo test

which simultaneously detects the viral protein p24, as well as antibodies (both IgM and IgG) to HIV-1 (including group O) and HIV-2.  When the test detects HIV p24 antigen (which appears earlier) or/and HIV antibodies (which appears later), it is considered a positive result. The duo detection ability (antigen/antibody) allows the test to identify early acute and chronic HIV-1 and HIV-2 infection, during or after seroconversion and is currently the gold standard for the diagnosis of acute and chronic HIV infections. The 4th generation HIV p24 antigen/antibody test has a reported average window period of 14 - 21 days, which may vary upon different individuals’ immune response.

Fourth-generation laboratory tests reliably exclude HIV by 45 days post-exposure, and this should be the window period applied when utilising these tests. [BHIVA/BASHH/BIA Adult HIV Testing Guidelines 2020]

Window Period of HIV p24 combo Test

14 days after exposure

(Ref: Paul R. Wratil et. Al. 2020 Comparative multi-assay evaluation of Determine™ HIV-1/2 Ag/Ab Combo rapid diagnostic tests in acute and chronic HIV infection. Med Microbiol Immunol. 2020; 209(2): 139–150.).
(Ref: Darlene Taylor et. Al. (2014) Probability of a false-negative HIV antibody test result during the window period: a tool for pre- and post-test counselling. Int J STD AIDS. 2015 Mar;26(4):215-24.)

Rapid HIV antibody test (quick test)

which only detects HIV antibodies in blood or oral fluid (not saliva) and can take 23 to 90 days to detect HIV infection after a possible exposure. Both the 2nd generation rapid HIV test (detects IgG antibody) and the 3rd generation rapid HIV antibody tests (detects both IgM and IgG antibody) are commonly used. Research shows that 99% of individuals infected with HIV would have detectable antibody level from blood at 57 days post exposure and 100% of HIV-infected individuals would have detectable antibody level from finger prick blood at 90 days after exposure.

Window period of HIV Quick Test

90 days after exposure

(REF: Kevin P. Delaney et al. (2017) Time Until Emergence of HIV Test Reactivity Following Infection With HIV-1: Implications for Interpreting Test Results and Retesting After Exposure Clinical Infectious Diseases, Volume 64, Issue 1, 1 January 2017, Pages 53–59)
(Ref. Delaney KP et al. Time from HIV infection to earliest detection for 4 FDA-approved point-of-care tests. Conference on Retroviruses and Opportunistic Infections, abstract 565, 2018.)

Our rapid test provided is approved by the WHO pre-qualification programme, which means it reaches the unified standards of quality, safety and efficacy for HIV/AIDS, which indicates the product of consistent quality in accordance with international standards and WHO/UNFPA specifications. 

The rapid HIV antibody test is used for screening purpose only. If the rapid test result is positive, a follow-up confirmatory test (using venous blood and performed in a laboratory) should be performed to confirmed HIV infection.

HIV Test List for HIV Detection

Our centre provide fast results, NOT WITH DAYS.

  • HIV RNA Quantitive Test - 4-8 hours* turnaround time
  • HIV p24 Antigen & Antibody Combo Test - 4-16 hours* turnaround time
  • HIV Quick Test - 15 minutes

*Test should be completed at or before 4pm.

Test ItemsPrice
HIV p24 Antigen Antibody Combo Test$390
HIV RNA Quantitive Test$1,450
HIV Quick Test$290

How to deal with HIV Result

A negative HIV result. This means that you are not infected with HIV. You may consider taking preventive measures to reduce your risk of HIV infection, such as practice safe sex, use condoms or pre-exposure prophylaxis (PrEP).
A positive HIV result. If the result of your confirmatory HIV test is positive, that means you have HIV (HIV positive). You should consult a doctor and get started on anti-retroviral therapy (ART) as soon as possible.

Although there is no cure for HIV, ART can suppress viral replication, protect your immune system and stop HIV from progressing to AIDS. You should regularly monitor your viral load (amount of HIV) and CD4+ cell count (reflects the state of your immune system) regularly to make sure your medication is working effectively. 

If you take ART as prescribed and maintain an undetectable viral load, you can stay healthy for years and will not transmit HIV to others even during unprotected sex (undetectable = untransmittable).



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