# FIV- False positive?



## pipje (Jun 29, 2011)

I brought my queen for her FIV/FeLV test today and there was a faint line in the FIV section which means she basically tested positive! The vet said it's probably be a faulty test, she will call the company on Monday. I asked if she could do another test now but she did not want to as she thought Pipje was moody when she was drawing blood.

I just can't believe it's a positive as Pipje's never been out and always tested negative. She has no exposure to other cats except 3 others all of whom are indoor-only cats at my home. She did visit a stud last year (unsuccessful mating) but he was tested too (although of course studs are only tested once a year). He is also indoor only. 

Google gives me mixed results in regards to reliability of the test. Some sites say positives are only possible if the cat was vaccinated against FIV(Pipje is not), some say there is a 20% chance of being a false positive. Have yours ever tested positive and was later found to be negative?

I would be devastated if she was truly positive(((((( she seems very healthy for now but have heard that FIV cats can seem healthy too initially so who knows!?


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## Ceiling Kitty (Mar 7, 2010)

I'm assuming this was a SNAP test?

These tests are, as I'm sure you already know, not 100% accurate; a proportion of positive (or negative) results will be false. What proportion? That depends on the population of cats you are testing.

In a population of cats likely to have a high prevalence of FIV (such as a group of feral tom cats), more of the positive results will be true than false. The opposite is true in a population of cats likely to have a low prevalence of FIV (such as indoor pedigree cats): more of those positive results will be false than true.

These tests are generally regarded as reliable when performed correctly, but they can never be 100% accurate. This is why positive results should be confirmed with a more definitive test such as IF or Western blotting (I like Glasgow vet school's lab for these tests). This could be a faulty SNAP test your vet has got, or it could just be a 'normal' false positive as we expect in a percentage of cats. Hopefully it is not a true positive.

The manufacturers will probably tell your vet to follow up on Pipje's result with a confirmatory test.

Fingers crossed all is well. Please don't worry yet! xxx


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## pipje (Jun 29, 2011)

Hi Ceiling Kitty,

It was a a SNAP test of sorts but not by Idexx. I can't remember the brand, it might have been Fasifil or something similar. It was white and the lines were pink. 

I really hope it was a false positive. No choice but to suffer through the weekend!


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## carly87 (Feb 11, 2011)

I wouldn't worry too much. Elisa can be quite inaccurate. I'd have her retested with an IFA.


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## havoc (Dec 8, 2008)

I've known of quite a few faint false positives. You wait a few weeks and test again. I've never heard of a false negative but then who would look further into a negative result? I'd be interested to hear of a situation where anyone has first hand experience of checking to see if a negative result was wrong and how they went about further testing.


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## pipje (Jun 29, 2011)

I have an appointment with another practice which opens on Saturdays. She's in heat now so if it was a false positive, I'd like to take her to the stud.

I'm keeping my mind open but I'm convinced the first test was faulty because part of the test strip was bright pink (not the lines)


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## pipje (Jun 29, 2011)

So relieved! The test (SNAPP from Idexx) done today was clearly negative!


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## OrientalSlave (Jan 26, 2012)




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## gskinner123 (Mar 10, 2010)

You have to wonder how some (?) of these snap tests are still on the market considering they're either over sensitive to very minor operator error or simply give too high a rate of false positives. A novice breeder and myself had a terribly worrying week over this. The owner has two 7 year old neutered sisters (both retired breeding queens, bred by me) that she has owned for several years, two 10 month old sisters bred by me and a 10 month old female from another breeder.

In anticipation of the two girls from myself going to stud in a few months or so, both were snap tested for FeLV/FIV. One was negative for both, the other neg for FIV, positive for FeLV. They ran the test again, still a strong positive. Blood sent to Glasgow for testing (PCR or IFA, can't recall). Meantime, the older neutered sisters and the other kitten were tested; one was negative for both, two positive for FIV. Glasgow''s result for the initial FeLV positive was negative and I've no doubt that the results will be the same for bloods just sent to them to check the other girls' results.

It has cost her a week of anguish and close to £500, some of which her vet is going to refund, if the FIV results are, as we expect, negative.


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## pipje (Jun 29, 2011)

gskinner: makes you wonder how reliable these tests really are and if they should be recognised. I hope your girls are fine, they most likely are. Even amongst cats who go out, FIV is relatively rare in NL (I assume Europe too) so I was really shocked when the vet said she tested positive and knew it was most likely a mistake. 

May I ask what brand the breeder friend's vet was using? The faulty one my get used was Fasisi (a German brand). The second opinion vet used SNAP by Idexx.


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## gskinner123 (Mar 10, 2010)

The FIV tests also came back as negative from Glasgow (the lab there is considered of one of the 'gold standard' testing facilities in the UK).

My friend did tell me the brand (I'd specifically asked because my own vet wanted to know) but I can't recall; the name wasn't familiar to me but definitely wasn't Idexx. I will ask her again. Either way, it gave 50% false positives which is dreadful though cannot rule out user error obviously.


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## QOTN (Jan 3, 2014)

gskinner123 said:


> The FIV tests also came back as negative from Glasgow (the lab there is considered of one of the 'gold standard' testing facilities in the UK).
> 
> My friend did tell me the brand (I'd specifically asked because my own vet wanted to know) but I can't recall; the name wasn't familiar to me but definitely wasn't Idexx. I will ask her again. Either way, it gave 50% false positives which is dreadful though cannot rule out user error obviously.


Have you seen this comparison of different tests? They do differ in accuracy but it is not a new assessment so perhaps the more inaccurate tests have been improved since it was done.


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## Ceiling Kitty (Mar 7, 2010)

Remember the accuracy varies depending on the population you're testing.


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## gskinner123 (Mar 10, 2010)

QOTN said:


> Have you seen this comparison of different tests? They do differ in accuracy but it is not a new assessment so perhaps the more inaccurate tests have been improved since it was done.


I thought I had (frantically!) managed to Google everything in existence last week but I'd missed that. Thank you, I will have a read.


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