Effect Of Antiviral Medication On Test Results

[jaxnoles]

My wife was taking 1000mg of FAMVIR for 7 days (for known/existing HSV-1 breakout) prior to her taking a Herpeselect test.  She noticed bumps on her vagina and we went to the doctor for a viral test.  That same day they drew blood for a Herpeselect test. The viral came back positive for HSV-2, the Herpeselect came back positive for HSV-1 and negative for HSV-2.  I was also tested (Herpeselct) twice in a four week period and came back negative for HSV-2 both times.  We were naturally both confused.  My question is what effect could the FAMVIR have had on her Herpeselect test result.  I understand that if she recently acquired HSV-2 that it would take time for the antibodies to develop and for the test to be positive, but since I was negative both times we assumed that she had been carrying HSV-2 for some time (this was the first incident of a break out on her vagina).  We did some research that mentioned that antiviral medications may effect the test results but we could not find anything specific on what exactly that meant.  Is it safe to assume that she had been carrying HSV-2 for some time (i.e., years) and that her taking FAMVIR at the time of her blood draw is what caused the negative HSV-2 result on the Herpeselect test?

[H. Hunter Handsfield, M.D.]

The only tests affected by antiviral drugs are those that detect the virus itself, e.g. culture of a lesion--and that's a sign the drug is working, i.e. suppressing the virus in the lesion.  The anti-herpetic drugs do not affect blood test results at all.

So I also am somewhat confused by your test results.  Conceivably your wife's genital area culture was mis-diagnosed as HSV-2 and really is HSV-1.  The only other explanation is that your wife acquired HSV-2 while on famciclovir (Famvir), which is exceedingly unlikely; and she would have had to have acquired it from you (unlikely with your negative HSV-2 blood test) or from another partner--and presumably you would have said something if that was likely.  So I am left with the possibility that one or the other of you has had false-negative HSV-2 results on your HerpeSelect tests.  That isn't common, but it happens.

Bottom lines:  1) Ask your wife's HCP and/or the lab to double check the HSV-2 determination for her positive culture.  2) If her isolate is confirmed as HSV-2, you both should have repeat testing.  If your provider(s) send specimens directly to Focus Technologies (manufacturer of HerpeSelect) and explain the situation, they may to special testing, such as Western blot, at no cost.  Alternatively, request a Western blot test by a reference lab, such as the University of Washington labs in Seattle.

PS:  Just curious whether you are sure your wife is on famciclovir and not valacyclovir (Valtrex).  The dose you describe is a peculiar one for fam but the typical one for val.  Also, famciclovir must be taken at least 3 times a day to be effective; even a large dose like 1000 mg likely isn't going to be effective if taken only once daily.

Good luck--  HHH, MD

[jaxnoles]

I think I mistated, or was confused; she had previously only used Valtrex for the oral HSV-1 but then started taking Famvir during the vaginal outbreaks, so I was not 100% sure as to whether she was on Famvir or Valtrex at the time of the culture diagnosis. When she received the HSV-2 positive culture it was during her second outbreak (second one within 2 weeks).  She then had a third outbreak two weeks later and has had nothing since (been about 8 weeks since the third outbreak).  The first outbreak was the worst and each one has been less painful and less in duration.