-Original Message-
We earlier did a snap ELISA test for my 16 yrs old indoor late stage CKD girl, Meowko, which was positive. But We just got her confirmatory IFA test back on Thursday, which is negative. In order to confirm whether the first snap test was false positive, we did the snap test again. The result was still positive (although we were told that it is "slightly" positive, I am not sure what this means...I guess it is like pregnancy test's faint line? ) Before all these tests, Meowko was tested twice negative when we adopted her and received vaccines.
I was wondering if anyone on this list has experience with contradictory results on snap and IFA tests? or if you have any thoughts on what we can read out of these tests? Can the contradictory results provide any clues for Meowko's current virus infection situation and therefore treatment possibilities?
Any thoughts and advice are appreciated. Thank you very much.
with my best,
Catherine (& Meowko)
Hi Catherine,
As far as I'm concerned, testing is the most confusing aspect of a confusing disease. Here's some of what I've found;
From UCDavis;
"What additional tests are available?
Cats testing positive by the ELISA test on serum should ideally be retested either using an ELISA test from a different manufacturer or by sending the appropriate sample for an IFA test at a diagnostic laboratory. If both tests are positive, the cat is very likely persistently infected. To be absolutely certain, cats can be held and retested after 30 days if resources are available and the cat can be appropriately housed and isolated (for the protection of the cat and population; see below). Because the IFA is less sensitive (more prone to false negatives) than the ELISA test, a negative IFA result in a cat testing positive ELISA can not be taken as an indicator that the cat is not infected. If the ELISA test is positive but the IFA results in a negative result, both tests can be repeated in 30 days. If this strategy is used, a plan should be made at the outset and clearly communicated to staff and foster parents regarding what will happen with cats that test persistently positive after the 30 day hold. A PCR test can also be run to help resolve any conflicts in the tests. PCR is very sensitive, so a negative test result run by a reputable laboratory indicates infection is unlikely. However, because PCR testing is very sensitive to laboratory error, correct sample handling and laboratory quality are extremely important."
Here's the whole treatise;
http://www.sheltermedicine.com/node/43
I have become convinced that a negative test means nothing. A positive test means a current infection, but that may, or may not continue. 18 months ago, I had a houseful of "negative" cats. Now I have 2 positive. I don't know how it started, or with who, or even when.
I am now vaccinating (with rFeLV vaccine) cats that are new introductions and test negative, but I'm afraid it's a an exercise in futility.
All the best,
Margo
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