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Question about PCR RNA HIV test
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Question about PCR RNA HIV test

Dear Dr. Sean,

Hope you are well and thank you for helping all of us here in the forum.

I am in a situation fairly typical of a significant group of posters here. I am a straight male who had a one time unprotected oral and unprotected vaginal sexual encounter with a 22 year old girl from Beijing. Not sure if relevant but she is an educated girl who claimed she only had 2 previous sexual partners.

I had tested myself for HIV and other STDs prior to this encounter and was negative on all counts. After this said encounter, I asked the girl if she had checked herself before and she said she has not.

Exactly 7 days (and 6 hours) after the encounter, I took a PCR RNA HIV test which has a limit of detection (LoD) of 100 IU/ml. I have been reassured by the doctor administrating that test that a result from this test 7 days post encounter is as conclusive as i need to worry myself with. Now I have read countless articles on the Internet since to verify this and cannot seem to reconcile the doctor's advice with what I see in other scholarly articles.

1. Isn't the eclipse period for any PCR RNA tests between 7 - 21 days with a median of 10 days?

2. I notice you start testing patients at your clinic with a PCR RNA test 7 days post exposure. What kind of ballpark accuracy (75%? 90% more, less?) would you prescribe to a negative result from such a test?

3. From previous posts you replied to, you seem confident of a negative PCR RNA result post 7 days. This seems contrary to the prescribed eclipse period I read about in (1) and also different from the CDC's recommended 9-11 day wait. Would you mind helping me reconcile this please?

4. For my piece of mind, can you please help me understand the overall risk I am in for HIV, in terms of the patients you see? i.e. how many heterosexual men have contracted HIV from a one off unprotected vaginal exposure?

Thank you very much for your help
Thank you for your post and welcome to our forum.  I will try to answer each of your questions here below:
1.) That is correct.  However HIV RNA is already detectable at 7 days with a high level of reliability of around 99%.
2.) Our lab gives us figures of an accuracy of 99% at 7 days.
3.) We follow UK guidelines.  At 7 days, it has an estimated reliability of 99%, which increases with time and after 10 days, this would be over 99%.  If we combine this with a relatively low risk sexual encounter like yours, we could consider a negative result to be conclusive.  However current UK guidelines would still recommend a follow-up HIV Duo test affter 4 weeks, even though in practical terms this might not be necessary.
4.) The estimated risk of a heterosexual man having unprotected vaginal intercourse with a known HIV positive woman is less than 1 in 1,000.  If the status of the lady is unknown and this is in the UK, this will be less than 1 in 1 million as there are only about 40,000 women who are positive in this country.
Best wisehs,
Dr José
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