[Question #1632] hib ag/ab combo test and hiv 2 and pcr

82 months ago
hello doctor hunter thank you for the wonderful service i will get straight to the scenario

i am male unprotected encounter with a female of unkown status (condom broke) thailand  

i pulled in a few seconds .

however i am paranoid so i want to know about accuracy of tests

1. took a ag/ab combo assay  from abbott at 14 days  how reliable is this in terms of percentage  ?

2. i have a pcr viral load/quantitation available at the clinic  is that same as nuclic acid test ? is pcr test which im mentioning conclusive after 2 weeks ?

3. my clinic has combo test for ag ab combo assay  (simultaneous detection for p24antigen and hiv1 and 2  but cannot distinguish which one is positive or negative )  . is that 4th generation test ? 

4. is this test ag/ab combo  conclusive at 28 days for hiv 2  also ?

thanks for the time

H. Hunter Handsfield, MD
82 months ago
Welcome to the forum. Thanks for your question and your confidence in our services.

First, congratulations for using a condom. Too bad it broke, but it still reflects your undertanding and wisdom about safe sex. Second, I will remind you that HIV is very inefficiently transmitted. The average risk for the male partner after a single episode of vaginal sex with an infected woman has been calculated to average about once for every 2,000 exposures. When we also consider the probability your partner had HIV (probably under 1% chance, or maybe as high as 5% if she is a sex worker) and only a few seconds expousre after the condom break, the chance you were infected probably was under 1 in a 100,000, perhaps less than 1 in a million. So you should be pretty relaxed and definitely can expect additional HIV test results to remain negative. To your specific questions:

1) A negative 4th generation (antigen-antibody, combo) test is probably around 80-90% reliable at 2 weeks.

2) PCR indeed is a nucleic acid amplification test (NAAT) and probably detects 90-95% of infections at two weeks. In other words, it would only slightly improve on the performance of the 4th gen test. In my opinion, you should not do it; not worth the high cost.

3) Yes, this is the 4th generation test.

4) In theory, the test might not detect all HIV2 infections at 4 weeks, but very nearly so and in the real world a negative result at 4 weeks is considered conclusive for both HIV1 and HIV2. In any case, my understanding is that HIV2 remains rare in Thailand. It's really a significant issue only in the areas of east Africa where HIV2 evolved; few cases are showing up in the rest of the world. There may be a few exceptions, but not (to my knowledge) in Thailand.

My advice is that you have one more 4th generation test at 4 weeks, which will be negative. No other testing is necessary.

I'll add that you probably are at significantly higher risk of gonorrhea, chlamydia, and syphilis than you were for HIV. Consider these tests as well.

I hope this information has been helpful. Let me know if anything isn't clear. Best regards and stay safe--  HHH, MD

82 months ago
Thank you for the response

14 days is very encouraging. Thank you

Pcr Viral load /quantitaion = naat test thanks for that won't have it

At 4weeks you say in the real world the ag/ab combo is conclusive for HIV 2 also . May I consider testing at 4weeks for HIV1/2 conclusive and not chase additional testing after 4weeks for HIv 2  ?

There is no second window period after 4weeks and just forget about it ?

My lab had combo test which said combine test for p24 antigen ,hiv1 and 2 . It doesn't matter that I don't have a separate result only for p24 antigen ? The combo detects both p24 antigen and antibody ( just making sure that I am tested for p24antigen as lab says this is combo for ag/ab and it detects p24 but you can't have a separate result )

I have zero symptoms at 3week mark is that also encouraging ?

I will go at exactly 28 days . I can be confident a negative result even though I was early ?

for the other stds, can you please mention when to test thanks again
H. Hunter Handsfield, MD
82 months ago
As I said above, "a negative result at 4 weeks is considered conclusive for both HIV1 and HIV2". There is no such thing as a second window period. It is the antibody that clears p24 antigen from the blood and makes that part of the test negative. Therefore, once a 4th generation test is positive -- usually by 2-3 weeks, always by 4 weeks -- it remains positive for life. It cannot again turn negative then positive again.

No, it does not matter that you do not have separate p24 antigen and antibody results. The test result is normally reported without distinguishing between them. If positive, one or both is present. There is no need to know which, and the test is not designed to report separate results.

Test again at 28 days. That's all. You can expect another negative result.

82 months ago
Thanks for the clarification regarding the combo test doctor

I got anxious and got tested at 20days with ag/ab combo and the result was negative
Will go again on the 28th day

At 20 days is my negative test more  encouraging ? What would you think at this time with a negative
Test at 20 days ?

Also with no ars symptoms present at 20days is that also a good sign ?

Thanks for all the help will go again on 28days
H. Hunter Handsfield, MD
82 months ago
At 20 days the result is nearly conclusive, probably around 97-98%. Absence of symptoms is also a good sign.

That completes the two follow-up comments and replies normally included with each question. However, I'll leave this thread open so you can report your result 4 weeks after the exposure. It will be negative. Let's not have any further discussion until then. Thanks.

82 months ago
Thank you doctor. Much appreciated

Just a quick update. I went on the 28th day  and the result was negative.

I also requested for a separate result for p24antigen but the medical lab  informed me that my previous test was a combined test ag/ab combo

I hope that the 28th day 15 minutes test is conclusive.

Also I've experienced zero symptoms in the past 28 days.

Many thanks for all the help and would appreciate your final thoughts on the conclusiveness of the 28 days 15 minutes test.
H. Hunter Handsfield, MD
82 months ago
Your reault is conclusive. I agree there was no need and would have been no benefit to a separate antigen test. You can move on with 100% confidence you do not have HIV. Don't have any more tests.

I hope the discussion ahs been helpful. Best wishes and stay safe.