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Had protected vaginal and oral sex. DNA PCR test negative. Got a Hepatitis B vaccination. Do I need to do further tests?

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Infectious Diseases Specialist
Practicing since : 2000
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I am from India and on a recent vacation to East Asia I did something stupid and visited a soapy massage parlour. I got a full body soapy massage followed by protected vaginal and protected oral sex. As far as I know the condom remained intact. However after protected vaginal sex the girl removed my condom and then used the same hands to give me a handjob for a few minutes and then I gave myself a handjob. As far as I can understand my risk level was low but I tend to worry too much.

So at 10 days I got a DNA PCR test which came back negative. At 27 days post exposure I got a HIV P24 Antigen and AntiBody test which came back negative. Both were from SRL Labs. UK medical websites say this is 99.8% accurate at 28 days. Is my test at Day 27 any less accurate? Can I stop worrying or do I need further tests? Today (1 month post exposure) I got a Hepatitis B vaccination, will this interfere with any HIV tests I take?
Posted Sat, 13 Jul 2013 in Sexually Transmitted Diseases
Answered by Dr. Binod Kumar Pati 47 minutes later

Thanks for your query.

From your clinical history it seems your risk to contract HIV is very remote, if at all she is HIV positive.

From the investigation results I can tell you that DNA PCR (Polymerase Chain Reaction) and P24 Ag detection are very sensitive tests. DNA PCR has a sensitivity to detect a single copy from 0000 mononuclear cells.

So over all I don't find anything for which you should be worried. If you are still anxious test your serum for presence of anti HIV antibodies after around 6-8 weeks of the suspected exposure, followed by a western blot, which is actually gold standard.

No, Hep B vaccination will not interfere with a HIV test.

Hope, Everything is clear.

Have a nice day.
Above answer was peer-reviewed by
Follow-up: Had protected vaginal and oral sex. DNA PCR test negative. Got a Hepatitis B vaccination. Do I need to do further tests? 18 hours later
Thank you Doctor for your prompt reply.

On many UK and Singapore Health Websites they say a negative HIV P24 Antigen and AntiBody test is conclusive at 28 days. Do you think I need further testing from a medical perspective or is it just for psychological comfort?
Answered by Dr. Binod Kumar Pati 22 hours later
Welcome once again.

The one day gap will hardly make any difference.
Though the p24 antigen is detectable from approximately 2 weeks after infection, a negative p24 result does not exclude HIV infection. How ever a positive test result is very specific for HIV.
Around 10 pg/ml of antigen has to be there in blood for the test to detect. This amount of antigen sometimes may not be present in HIV infected patients, even when the virus is actively replicating.
Also development of high level of HIV-specific antibodies form a complex with p24 antigen making it undetectable.

There are procedures to dissociate antigen-antibody complexes and then to detect p24 antigen, but still the antigen remains undetectable in most asymptomatic patients.

Considering all these your were suggested to go for HIV antibody testing, if very much anxious. Because once developed, antibody is detectable persistently, though antigen may become undetectable during the course of the disease.

Hope the rationale is understood.
You may close the discussion and rate it if satisfied.
Have a nice day.
Above answer was peer-reviewed by
Follow-up: Had protected vaginal and oral sex. DNA PCR test negative. Got a Hepatitis B vaccination. Do I need to do further tests? 1 hour later
Thank you once again for your reply. I think there has been a mis understanding. I stated that at day 27 I got a p24 antigen AND anttibodies 1&2 test. Both came negative. The logic being that even if one is present one might be infected. Taking this into account is there any need to retest ?
Answered by Dr. Binod Kumar Pati 36 minutes later
If we are testing at the wrong time there is no use of the result.
HIV antibodies usually develop in 3 - 6 weeks and invariably in all infected persons within 12 weeks. In between 3-12 weeks we may get a nonreactive test, not because of absence of antibodies, but rather due to undetectable level in serum. Hence was the suggestion to go only for retesting for anti HIV antibodies. No need to repeat others.

I hope It's clear now.
Above answer was peer-reviewed by
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