[Question #6980] would antihistamine affect HIV window period?

8 months ago
Hello, 

              I had a question, I took OTC Antihistamine/Antacid, (Tagamet). Would taking that affect the 6-12 week window period(Generation 4 HIV test) ? Even if I was taking it during the time of the test?  My results were non-reactive. I read that antihistamines are a immunosuppressant

Thank You!
8 months ago
hello, sorry to double post but after some quick research I found this : "You may be familiar with cimetidine (brand name, Tagamet®) as a drug sold over the counter in pharmacies to combat heartburn. But cimetidine has the unexpected beneficial side effect of boosting immune function. It does this by reducing the activity of T-suppressor cells, an action that prevents the immune system from prematurely shutting down a needed immune response"

https://www.lifeextension.com/magazine/2017/2/winterize-your-immune-defenses

So which is it? Is it considered an immunosuppressant or not? thanks!
H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
8 months ago
Welcome to the forum. Apologies for the slightly longer than usual response time.

There are no medications of any kind -- whether immune suppressing or boosting -- that have any effect whatsoever on test results timing or reliability of the current HIV antibody (third generation) or antigen-antibody (AgAb, 4th generation) blood test. That's an urban myth left over from the earliest HIV antibody tests no longer in use. The third and fourth generation tests are unaffected even by the most potent immune sypressiing drugs or chemotherapy. In any case, the antihistamines are not considered to have significant immune suppressing or boosting effects. I would suggest limiting your online research to medical and scientific resources. (The statement you quote doesn't make much scientific sense to me!) 

The HIV antigen-antibody (AgAb, 4th generation) blood tests detect 100% of HIV infections 6 weeks or more after the last possible exposure. Assuming your exposure was that long before you tested, your negative result is conclusive. Taking cimetidine had no effect on it.

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

HHH, MD
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8 months ago
Yes my blood test was months after my possible exposure. I had two quick follow up questions if you don't mind. 1) Once antibodies are active, is there anything that can make them become undetectible again? (medications etc.) Or once they're detectible, they're detectible for life? 2) Aside from Biotin, do you know anything that can interfere with the Generation 4 test? (I know companies like Roche explain not to take biotin before their Generation 4 test). Also, it states not to take biotin before an HIV test right on Labcorps site...but it doesn't mention anything else. 

Thanks!
H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
8 months ago
1) The AgAb tests invariably remain positive for life. Once present, antibody is always detectable. If for some reason it were not (I've never heard of this happening), the antigen portion of the test would be positive.

2) See my comment abov e about "no medications of any kind". That includes biotin. My understanding is that the warning is based on theoretical considerations, with no actual evidence or reported cases of interference with HIV testing. Once FDA issues such a statement, no matter how unlikely, for legal reasons testing companies and agencies feel obligated to give their warnings. I am unaware it has actually ever proved to be a problem.
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8 months ago
gotcha, not trying to argue with you. But on Roche's site itself it says there is interference above 5MG...but again...Im not a scientist or anyone who runs the machines so Im just going by what I found. Either way I thank you for your time. Just to confirm: No meds will alter my bodies ability to create antibodies. So a generation 4 test 8 weeks out is conclusive...no matter if I was taking anything or not? and there is no reason for me to retest (considering that was my last possible exposure) correct? 

I thank you again for your time as I know this is my last question. 
H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
8 months ago
Your "Just to confirm" statements are entirely correct.

That completes the two follow-up exchanges included with each question and so ends this thread. Thanks for the thanks; that's why we're here!
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