[Question #2589] question for Dr. Hansfield re whether taking valtrex affects hsv2 testing

43 months ago
Dear Dr. Hansfield,
I have been taking Valtrex daily for over a year. I had an outbreak of what appeared to be herpes. Swab came back negative. Just had immunoblot done with negative result for both hsv 1 and hsv2. I am perplexed because I know for certain that I have hsv1. I used to get cold sores often when I was younger. Therefore, has taking valtrex affected the results? And if so, how? How can a viral suppressant result in antibodies not being detectable?  LF
Terri Warren, RN, Nurse Practitioner
Terri Warren, RN, Nurse Practitioner
43 months ago
Hi, I answer the herpes questions on this forum. 
The IgG test for HSV 1 misses 30% of infections so it is not very surprising that the immunoblot missed your HSV 1 infection. 
Were you taking the Valtrex for your cold sores or for what appeared to be a herpes outbreak? If you take antivirals with a first infection and you take them continuously, you can most certainly postpone antibody development for months or even years.  So let's clarify - are you thinking that you acquired new genital herpes and you were taking antiviral for that and continuously?  The purpose of antivirals is to prevent viral replication. If it's doing a terrific job at that, there will be little virus around and thus the immune system can't see the virus and make an antibody response.  Does that make sense? 

It's also possible that the lesion was not herpetic. 

Terri
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43 months ago
Thank you for your response. I had no idea that igg test for hsv1 misses 30%. From everything I've read, I thought the accuracy was quite high, like 99%! Yes you are correct, I am taking the antivirals for what I believe to be herpes, continuously from when I had my first apparent outbreak over a year ago. So if it's the case that the antiviral has resulted in minimal antibodies, I suppose I should stop taking the valtrex and be re-tested. How long do I need to be off the valtrex? I've read 12 weeks. Does that have to be continuous? Can I count the first four weeks between the time of exposure and when I started valtrex?
Terri Warren, RN, Nurse Practitioner
Terri Warren, RN, Nurse Practitioner
43 months ago
I would agree that 12 weeks being off medication would be appropriate for the western blot to be done.  And yes,you can count the first four weeks as that time frame would have given you some opportunity to start producing antibody

Terri
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43 months ago
Actually it's the immunoblot, not western blot, does that make a difference? And what is the sensitivity for hsv2 with immunoblot? Thank you!!
Terri Warren, RN, Nurse Practitioner
Terri Warren, RN, Nurse Practitioner
43 months ago
The immunoblot is an inferior test simply because it does not give us an index value to identify a possible false positive. We are concerned about false positives for people with index values between 1.1 and 3.5. Unfortunately, the immunoblot does not provide that opportunity.  It simply gives a positive or negative results. The sensitivity of a similar test to the immunoblot for HSV-2 is about 92%. The Western blot is the gold standard and yields the sensitivity of greater than 99% for HSV-2. 

Terri
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