HIV tests

[Georgeroberts]

Hi doctor -

Ive come across several postings regarding PCR tests and false positives.  I recently ordered an early detection test from stdexpress.com or something like that, legit tests done by LabCorp, so I had a DNA PCR test done at 15 days post possible exposure. Now with this PCR test, if it's positive, they go on to do a western blot.  Now what I am wondering about is what would a positive PCR and negative western blot at 15 days mean.  I didn't get this result but would the western blot confirm the PCR at 15 days or too soon? I guess what I'm
Simply asking is if a western blot is specific/sensitive "good" that if it's negative, you are negative? Or would such a result possibly either be a false positive or mean that I haven't produced enough antibodies yet.  It's LabCorp so i assume it's all 4th gen tests.  Thanks.  Basically, how would you interpret a 15 day positive PCR, neg western blot? I am not sure if this is a possible outcome.  Thanks.

[Edward W Hook, MD]

Please re=read my answer.  I really don't want to guess what this means beyond telling you that it suggests that you do not have HIV.  Why not ask the peole who told you this is a good test.  I don't mean to be insensitve, but I feel storngly that if companies are going to use tests for something other than their recommended purpose, they should be prepared to tell you what the results mean.  EWH

[Georgeroberts]

Hi Doctor:

Thank you for the reply.  2 things:  I miscalculated and I tested at 11 days (not 15) and I just got the result and it was negative.  How definitive would you consider this?  What would you suggest for further testing if any?
Thank you.

[Edward W Hook, MD]

Before I answer your question, let me caution you about playing out this sort of "what if scenario" – this is not a fruitful course of action.  You have chosen to seek testing offered by a company that uses a well respected laboratory (LabCorp) to use tests in a way that they are not recommended.  Accepted HIV testing approaches and recommendations are based on the results of carefully conducted studies involving thousands, or even tens of thousands, of participants.  Because a substantial number of people are so very anxious to find out if they have acquired HIV a little sooner than they might if they followed recommended approaches, the labs offer the sort of testing approaches you describe.  I know little about your exposure history but for most people getting an HIV PCR does little harm and is simply a waste of money.  For the small proportion who get false positive results however, the PCR test, when used for diagnosis (something that it is not recommended for) causes trouble because of false positive tests.  Fortunately, these false positives are infrequent, but they do occur.  There are not high quality studies which define precisely when we can expect totally reliable PCR results after an exposure, nor what the meaning of a positive PCR and negative Western blot means just a few weeks after an exposure.  It would certainly be possible for someone who had recently acquired HIV to have a positive PCR and a negative Western blot however.  

if you get a negative PCR at 15 days, it probably means you did not get HIV.  If it's positive, then things need to be unraveled but let's wait and see what happens.  EWH