The IFA is definitely the test to trust but from what I understand if 
the first snap test is positive then you need to do further testing like
 the IFA and to be safe you really need two tests with the same results 
to know for sure.  You would need either two IFA tests a few months 
apart that are both 
negative or an IFA and another snap test that are both negative.  So if 
you do an IFA now and the results are negative then you should still 
wait and do another test later on.  Since your first snap test 
showed positive you could do an IFA now.  If the IFA is negative right now then 
next time, a few months later if possible, you do either a snap test or 
another IFA test and the result should be negative also.  It's really 
confusing because the different test look at different things but I 
would definitely trust an IFA over a snap test.

Here's how I understand how the virus works, of course this is from a 
lay perspective as I'm not in the medical field whatsoever:

After the cat has contracted the virus it will first be in his 
bloodstream and saliva and urine.  At this point the virus has not yet 
progressed into his white blood cells so the cat's immune system could 
still extinguish the virus before the virus really takes hold in the 
body.  A snap test right now would show positive but the IFA would be 
negative.  That's because the snap test looks to see if the virus is in 
the bloodstream but the IFA test looks to see if the virus is in the 
white blood cells.  After a certain amount of time, some say three 
months some say six months, the virus will either be extinguished or 
will have gone into the white blood cells.  If the virus has been 
extinguished then a snap test and an IFA test will both be negative.  
But if the immune system was not able to extinguish the virus and it has
 really taken hold of the cat and progressed into the white blood cells 
then both a snap test and an IFA test will be positive.  In this case 
the cat will never be able to extinguish the virus.  Once the virus has 
progressed from his bloodstream into his white blood cells he won't be 
able to get rid of the virus so if the IFA ever comes back positive then
 there's no need to do any more testing.  Does this make sense?  I could
 be wrong but from what I've read and gotten from vets this is how it 
goes.  Of course there's a third option where the cat's immune system 
puts the virus into dormancy but no need to go into that right now.

So never completely trust the snap test and if it ever comes out 
positive then more testing must be done.  What order and how much time 
you wait in between the tests are the variables.  If you think the first
 snap test was done incorrectly and the results were wrong then you 
could do another snap test.  If a second snap test comes out negative 
then probably the cats are fine and you don't need to do anymore 
testing.  It just means they did the first snap test wrong.  But, if a 
second snap test comes out positive then it means the virus is definitely in 
the bloodstream and you need to do an IFA test 
because it's not 
necessarily in the white blood cells.  Or, instead of doing that 
second snap test you could just do an IFA test.  If you assume the first
 snap test was done correctly and the positive reading was correct then 
don't bother with another snap test just do an IFA test to see if the 
virus has progressed from the bloodstream into the white blood cells.  
Like I said, the snap test means the virus is in the bloodstream but the
 IFA test is to see if the virus is into the white blood cells.  The 
results of the IFA test will tell you whether you need more testing 
after that.  I would only do a second snap before doing an IFA if I had a
 suspicion that the first snap test was done wrong for whatever reason.

I hope I made sense.  Lots of times I say too much and confuse 
everyone.  I did that in our rescue recently when we came across a 
positive nursing mother and I was trying to explain the testing 
procedures and what they mean.  We were trying to decide whether to do a
 second snap test or do an IFA right away or just wait a couple months 
and do an IFA then.   The mama and kittens weren't ready for adoption 
anyway so we just ended up waiting a couple months then doing an IFA on 
the mama cat.

“I am 
not interested to know whether vivisection produces results that are 
profitable to the human race or doesn’t….the pain which it inflicts upon
 unconsenting animals is the basis of my enmity toward it, and it is to 
me sufficient justification of the enmity without looking further.” – 
Mark Twain

> From:
> To:
> Date: Mon, 1 Aug 2011 18:57:26 -0700
> Subject: Re: [Felvtalk] doubts on two FeLV positive kitties
> If I may...
> The IFA is more expensive, but results are more reliable.  My vest advised, 
> "If the snap (vet's office) test is positive, you need to do IFA.  If the 
> snap is negative, you probably don't need IFA."
> Good for you for trying to be as sure as you can be.  And thank you for 
> helping our furry friends!
> Buena suerte!
> ~Bonnie
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