HIV Testing: Antigen and Antibody Detection Timelines

HIV testing issues?

Hello, I would like to inquire about the Abbott fourth-generation HIV Early test, which can detect both antigens and antibodies.
The antigen can be detected one month after exposure; however, regarding the antibody testing, can it still yield results if it has not been three months? Previously, antibody testing required a three-month window period.
I am currently 72 days post-exposure (10 weeks), and my test result was negative.
I would like to know if, at this point, the antigen would no longer be detectable after six weeks, and whether antibodies can be detected before the three-month mark.
I just want to confirm if this means I have ruled out the risk of infection.
During the 72-day period, I did not engage in any high-risk behaviors.
Should I still follow up with testing after three months?

j, 30~39 year old female. Ask Date: 2023/10/09

Dr. Lin Wufu reply Internal Medicine

Hello, the fourth-generation rapid test detects both antigens and antibodies.
It is expected that a positive result could be detected in about two weeks, but individual responses vary; some people may take three to four months to test positive.
(A positive result for either antigen or antibody is considered positive.) Therefore, it is currently recommended to follow up with the fourth-generation rapid test and continue testing for negative results for three to four months to reliably exclude the risk of infection.

Reply Date: 2023/10/09

More Info

Understanding HIV testing, particularly the timelines for antigen and antibody detection, is crucial for anyone who may be at risk of infection. The fourth-generation HIV tests, such as the Abbott ARCHITECT HIV Ag/Ab Combo test, are designed to detect both the HIV antigen (specifically the p24 antigen) and antibodies to HIV. This combination allows for earlier detection of HIV compared to antibody-only tests.

Antigen and Antibody Detection Timelines
1. Antigen Detection: The p24 antigen can typically be detected as early as 2 to 4 weeks after exposure to the virus. This means that if you were to take a fourth-generation test one month after a potential exposure, there is a good chance that the test could detect the p24 antigen if you were infected.

2. Antibody Detection: Antibodies to HIV usually take longer to develop. For most individuals, antibodies can be detected within 4 to 12 weeks after infection. The "window period" for antibody tests is generally considered to be around 3 months. This means that while some people may develop antibodies sooner, it is not uncommon for others to take longer.

Your Situation
In your case, you mentioned that you were tested 72 days (approximately 10 weeks) after a high-risk exposure, and the result was negative. At this point, you are within the window period for both antigen and antibody detection. Since you are beyond 6 weeks, the p24 antigen should still be detectable if you were infected, but the likelihood of detecting antibodies is less certain until you reach the 3-month mark.

- Antigen Testing: After 6 weeks, the p24 antigen may still be present, but its levels can decrease as the body starts to produce antibodies. Therefore, while you may still detect the antigen, it is not guaranteed.

- Antibody Testing: At 72 days, you are approaching the point where antibodies may be detectable, but it is still possible that you may not have developed them yet. The traditional recommendation has been to wait until at least 3 months post-exposure for a conclusive antibody test result.

Recommendations
Given your negative result at 72 days, it is a positive sign, but it does not completely rule out the possibility of infection. Here are some recommendations:
1. Follow-Up Testing: It is advisable to have a follow-up test at the 3-month mark. This will provide a more definitive answer regarding your HIV status. If you remain negative at that time, you can be more confident that you are not infected.

2. Regular Testing: If you are sexually active, especially with multiple partners or without protection, regular testing is recommended. The CDC suggests testing at least once a year for sexually active individuals, and more frequently (every 3 to 6 months) for those at higher risk.

3. Consult Healthcare Providers: If you have any concerns or experience symptoms that could be related to HIV, consult a healthcare provider for personalized advice and potential additional testing.

In summary, while your negative test at 72 days is encouraging, it is essential to follow up with another test at 3 months to ensure a conclusive result. Understanding the timelines for antigen and antibody detection can help you make informed decisions about your health and testing practices.

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