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Are the HIV p24 test results accurate? I have had anal sex and oral sex with a male partner.

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General & Family Physician
Practicing since : 2011
Answered : 243 Questions
I had a HIV P24 Duo test in Hong Kong 16 days after sex. The sex was safe but I slide my penis into my partners anus for about 1 sec and also my male partner came a little in my mouth. 9 days after sex I got some diahhorea for a few days and a rash on my chest and a sore throat. I went to a STD clinic here and they did the P24 test on day 16 and it was negative. Do you think I can be sure this result is accurate ?
Posted Wed, 2 May 2012 in Sexually Transmitted Diseases
Answered by Dr. Sapan J. Pandya 1 hour later
The HIV p24 antigen is an antigen to the core HIV viral protein. This antigen becomes detectable at approximately 10 days post exposure, peaks at 16 days or so and then remains at high level for 8 to 10 weeks post exposure.
So you got yourself checked at a very perfect time. And congratulations on being tested negative. A positive p24 then that generates a further panel of testing.
But a word of caution. Not every test is 100% accurate. Nobody claims so for HIV p24 Duo Test. It is one of best test for early diagnosis.
If you had bleeding in penis while attempting anal sex you are at risk, if your partner is infected. The penetration is important rather than 1 second time.
If you bit your partner while oral sex, and if you are infected yourself, then your saliva may infect him. His semen would infect you only if you have injuries / ulcers in your mouth.
So I believe that this result in accurate if your narration of the sexual activity is accurate. No test is 100% perfect.
Kindly do not persist in such high risk behaviour. The best thing is protection with condom.

Above answer was peer-reviewed by
Follow-up: Are the HIV p24 test results accurate? I have had anal sex and oral sex with a male partner. 1 hour later
Hi Doctor thanks for your answer. I read online that the manufacturer of the P24 duo test says that the P24 antigen test can detect hiv as early as 5 days post exposure, but I read they state 14 days post exposure to be sure. Is this true ? It certainly agrees with what you said about 16 days being the peak level for P24.

I am just scared as I have had nausea feelings, a slight sore throat (but no cough or cold) headache and a slight rash (more redness than any pattern) on my chest around my colar bone for the last 7 days. But I suppose these could be anxiety related. The doctor I saw on Monday said he did not think this rash was hiv rash, but I am not sure if its that east to recognise. I have taken my temp every day and its normal, I just took it and it was 35.2.

So I am hoping I am ok, and the guy I had sex with is going to get a hiv test on Wednesday which will reduce my anxiety if its negative. I might try and find a place that does the DNA PCR / RNA test here in Hong Kong to offer me more relief. But I am hoping from what I have read and what you said I am ok.

Do you think I should do a PCR / RNA test to be 100% sure ?
Answered by Dr. Sapan J. Pandya 5 hours later

There is some variation according to the kit used. But maximum chances lie on day 16.
HIV rash do not show so fast. It may be some seasonal virus.
You may go for PCR / RNA test only for relieving your anxiety.

Hope this answers your query.
Above answer was peer-reviewed by
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