[Question #6216] Testing after PEP

17 months ago
Hi Dr.

I had a potential exposure with trans CSW in south america nearly 11 weeks ago and started a 30 day course of PEP 60 hours post exposure. 

Tested with 4th gen DUO lab tests at 17 days (during PEP), and immediately after PEP.  Also tested 4/5/6 weeks post PEP with 4th gen lab tests.

Also tested 10 days post-PEP with RNA 'Early detection screen'.

Private doctor is telling me no further need to worry (BASHH guidelines state re-test 8-12 weeks post exposure).

Just looking for your opinion on my circumstances (whether I ought to still be worrying/testing). 

Is it safe to have sex (protected or unprotected) with my partner?

A week is a long time in post-PEP land. 


H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
17 months ago
Welcome. Thanks for your question and your confidence in our services.

In theory, PEP may delay the time to positive testing, if it doesn't work. However, whether this happens isn't entirely certain; and, if it does, the time to conclusive testing isn't certain. However, most experts agree 3 months is sufficient for the antigen-antibody (AgAb, 4th generation) blood test, even without RNA testing. With the negative RNA soon after PEP and negative AgAb 4.5 weeks and 6 weeks later, almost certainly you were not infected. However, to meet many experts' recommendation -- and to follow BASHH guidelines, whicn make sense to me -- you should have another AgAb test 12 weeks after completing PEP. However, the chance you have HIV is low enough that if somehow I were in your situation, I would resume sex with my wife without worry, but stil would have a final test at 12 weeks.

As for your closing comment, you are experiencing a downside of PEP that many people at risk and their doctors don't consider -- that PEP prolongs the period of axienty until testing can be conclusive. It's one of the main reasons that PEP should only be used for truly high risk encounters. I can't comment on whether PEP was wise in your case, not knowing the details about the exposure. But this is an issue for you (and other users) to consider should a similar circumstance arise in fhe tuture.

I hope these commetns are helpful. Let me know if anything isn't clear.

17 months ago
Thanks Dr.

The UK BASHH guidelines recommend retesting after PEP 8 to 12 weeks post exposure - so given a 4 week PEP regimen, that would be 4-8 weeks post PEP.  Some clinics seem to regard a 4 week test post-PEP sufficient.

I have another test booked (which the Dr has said he doesn't consider necessary) for 8 weeks post PEP (12.5 weeks post exposure). 

I understand the difference in opinions arise from interpretation of very limited data and from personal clinical experience. If I were your patient, would you consider the 12 week test (post exposure) conclusive?

I am curious about your advice about having sex with my partner. If the advice is that I ought to wait for another retest, this would suggest that there remains a probability that I could in fact be infected; would having sex not therefore put my partner at (albeit small) risk?

Thank you for your speedy reply - 
17 months ago
Hi again Dr.

I may as well add, that I also tested for:

Chlamydia and Gonorrhea urethral swab screen -- 2.5 weeks post exposure
HepC (RNA) -- 40 days post exposure
HepC Ag and HepB Ag --  8 weeks post exposure
Syphilis IgG IgM -- 10 weeks post exposure

Do you think any of these other STD require further testing? 
Can the PEP affect any of these test results?
Is there anything I have missed? 

H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
17 months ago
As my reply above implies, there simply are no solid data on the effect of PEP on test timing if PEP doesn't work. In absence of data, equally qualified experts have different opinions and advice. The BASHH guideline isn't necessarily wrong, but some experts advise 3 months after completion of PEP, and a few even advise 6 months. My own colleagues are in the 90 days after competing PEP camp, which is therefore my default recommendation. But 2 months per BASHH may be just fine. (The basic fact is that PEP is highly effective, so there are almost no reported cases of its failure -- and thus not enough patient experience to judge actual test performance. For the foreseeable future, all such guidelines will be based primarily on biological understanding and personal interpretion, without firm research to back them up.)

My advice about sex with your partner is based on the extremely unlikely chance you have HIV, low enough to take the chance of resuming sex, in my opinion -- with very low risk you would infect her. But I'm not you and cannot make that decision for you.

The other tests you had are completely reliable and are not affected by PEP. For what it's worth, I would have advised against viral hepatitis testing at all. But you should find all those results completely reassruing. I see no need for any other tests
17 months ago
Thanks again Dr for your thoughtful response.

To summarise:

1. My tests to date are very indicative, but not firmly conclusive in your view until 90 days after PEP.
2. I am conclusively clear of other STDs based on my previous (stated) test results.

Would a negative RNA test now be conclusive of being HIV free? Rather than having to wait another 6 weeks for Ab/Ag testing?

Have you encountered any patients in my situation that have tested negative 6 weeks after PEP only to test positive later?

17 months ago
I'd like to try to understand the logic of that theory --

If 45 days is regarded as sufficient without any PEP, why the period extends to 120+ days with PEP?

Is the theory that PEP can suppress immune response for weeks beyond finishing the course? Or that there may be a period of latency of the virus after PEP? Or simply cautious estimates based on unknowns.

I read a summary of a French study that tested participants that were on long term ART. All took a 'Drug Holiday' and were tested at different intervals. All participants had high detectable viral load within 4 weeks of stopping their medication. Clearly I'm no expert, but that would suggest to me that the virus rebounds very quickly after the cessation of anti-retrovirals.

I took some comfort in believing that after PEP, had there been any live virus, it would be detectable within the usual 6 week window period.

Alas, I think I know what your going to say: stop reading stuff I'm not qualified for, suck it up and wait.

H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
17 months ago
Be clear:  it is most likely that if PEP suppresses HIV without preventing infection, it becomes active witin 2-3 days of completing PEP, and at that time you can start the timeline to testing as if that were the date of exposure. That is, most likely RNA testing would be positive within a couple weeks and the AgAb test positive by 3-4 weeks (rarely as long as 6 weeks). IF so, there is no need for testing any later than normal, except to start the timeline at the end of PEP instead of at exposure.

However, some experts believe the timeline may be extended, and to date research has not refuted this possibility. I am not sufficiently expert to speculate with you about the biological mechanisms that might be at play if test positivity is delayed.  

My closing commet would have been stated a bit more diplomatically than your own, but you more or less have it! In the meantime, stop worrying so much. The chance you have HIV is exeedingly low, probably under one chance in many million. You can expect any additional tests to be negative.

That concludes the two follow-up comments and replies included with each question and so condludes this thread. I hope the disucssion has been helpful.