Update: Well, MaryChristine is dead right when she says the "...experts can't 
agree". My vet called me back in response to my request for a serum ELISA and 
said he has *never* had a problem with using whole blood (though he'll be happy 
to do serum if that's what's wanted). So basically he's at odds with the 
(feline-specialty) vet on his staff who had told me serum was the ONLY way to 
go! (I did tell him about the fact she and I had spoken and that she had been 
emphatic about using serum.) He went online to a "vet only" website while we 
were on the phone and pulled up a word doc (2003), and an email (2008). The 
relevant info in the word doc appears to favor serum, plasma, saliva & tears; 
the email is from Susan Little DVM. But she's not talking from her own 
experience, nor does she make a categoric statement that whole blood is as 
accurate. She does say there were concerns in the past about using whole blood 
but "doesn't think" that's the current case.
At any rate, I think we'll be doing an IFA next when funds allow. Unlike the 
vet on his staff, my vet didn't feel the necessity to start over with 
Kerry PS Not allowed to send the whole attachment to list, but if anyone wants 
it (possible outdated-ness notwithstanding) just let me have your private 
address and I'll forward.

Diagnostic Methods for Feline Viral Pathogens
ACVIM 2003
Melissa A. Kennedy, DVM, PhD, DACVM 
Knoxville, TN
Diagnosis of viral infections of cats can be a challenge for the practitioner. 
Identification of the infectious agent involved in a disease is important not 
only for determination of the best treatment protocol, but also in terms of 
control and prevention. The variety of diagnostic assays available, the advent 
of newer molecular assays, and the differing recommendations that may be 
offered from diagnostic laboratories can be confusing. Interpretation of the 
results of the assays used also may not be straightforward-results may vary 
with the sample, methodology, and laboratory utilized.
In an attempt to clarify some of the issues important in viral diagnostics, the 
general methodology of the available assays will be briefly described. 
Individual agents and the various diagnostic assays useful for each will be 
explained and include Feline Herpesvirus-1, Feline Calicivirus, Feline 
Parvovirus/Canine Parvovirus-2b, Feline Coronavirus, Feline Immunodeficiency 
Virus, and Feline Leukemia Virus.

Feline Leukemia Virus
Detection of viral antigen is the test of choice for feline leukemia virus. 
While viral antibody may be present, it does not provide information on whether 
the animal is persistently infected with the virus. Also, the use of the FeLV 
vaccine can complicate interpretation of results. The test used most commonly 
is the ELISA, of which there are a number available. This test assays for the 
p27 core antigen of FeLV and may be done on serum/plasma, saliva, or tears, 
depending upon the kit. IFA may also be used on whole blood smears. The ELISA 
is a sensitive assay, and can detect infection during the primary viremia. The 
majority of cats positive at this stage will go on to clear the virus, thus 
retesting of positive cats is required to determine the persistence of 
infection (2). IFA does not detect infection until the secondary viremia, after 
infection of precursor cells in the bone marrow; thus, animals positive by IFA 
are less likely to clear the virus (2). ELISA +, IFA-cats should be retested in 
2-3 months; ELISA -, IFA + cats are uncommon and should also be retested. False 
positive results occur at a significant rate among ELISA kits (4). This can be 
due to the use in some kits of mouse antibody to capture the FeLV antigen, and 
the presence of antibody to mouse immunoglobulin in some cats (2). False 
positive results with ELISA's have also been documented due to the use of whole 
blood. False positive results using IFA have been documented with some 
anticoagulants (2). Therefore, use of fresh whole blood to make the smears is 
recommended. PCR has been investigated for detection of latent infections in 
bone marrow, but has not proven superior to ELISA/IFA combinations (5). 

1.  Andrew, Stacy E. (2000), "Feline Infectious Peritonitis", in Veterinar 
Clinics of North America, Small Animal Practice, September, 30(5):987-1000.
2.  Barr, Margaret C. (1996), "FIV, FeLV, and FIPV: Interpretation and 
Misinterpretation of Serological Test Results", Sem. In Vet. Med. And Surg., 
August, 11(3): 144-153.
3.  Burgesser, Kent M., Stephanie Hotaling, Anita Schiebel, Scott E. Ashbaugh, 
Steven M. Roberts, and James K. Collins (1999), "Comparison of PCR, Virus 
Isolation, and, Indirect Fluorescent Antibody Staining in the Detection of 
Naturally Occurring Feline Herpesvirus Infections" , J. Vet. Diag. Invest., 
March, 11:122-126.
4.  Hartmann, K., R. M. Werner, H. Egberink, and O. Jarrett (2001), "Comparison 
of Six In-House Tests for the Rapid Diagnosis of Feline Immunodeficiency and 
Feline Leukaemia Virus Infections", Vet. Rec., September, 149:317-320.
5.  Herring, E. S., G. C. Troy, T. E. Toth, S. D. Forrester, L. A. Weigt, and 
I. P. Herring (2001), "Detection of Feline Leukaemia Virus in Blood and Bone 
Marrow of Cats with Varying Suspicion of Latent Infection", J. Fel. Med. and 
Surg., 3:133-141.

Kathryn Hahn on 09/24/2008 9:25:49 am ET

*Posted In Message Boards 2.0 

Hi there

Just a quick question...when running an Idexx snap test for FeLV/FIV is there a 
preference for using whole blood vs serum vs plasma for the most accurate test 

Thank you! 

Susan Little on 09/24/2008 2:02:40 pm ET

*Posted In Message Boards 2.0 

Here's what the test kit insert says about samples:

Serum, plasma or anticoagulated whole blood (e.g., EDTA, heparin), either fresh 
or stored at 2°-7°C (35°-45°F) for up to one week, can be used. For longer 
storage, serum or plasma can be frozen (-20°C/-4°F or colder) and then 
recentrifuged before use. Hemolyzed or lipemic samples will not affect results.

In the past, there were concerns that using whole blood caused more inaccurate 
or hard to read results with the in-clinic ELISA tests, but I don't think there 
is current evidence that this is the case for the IDEXX Snap test.

Susan Little DVM
Diplomate ABVP (Feline)
Ottawa, Canada

Roscoe Village Animal Hospital, P.C.
3131 North Clybourn Ave
Chicago, IL 60618

-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of MaryChristine
Sent: Saturday, November 22, 2008 8:09 PM
To: felvtalk@felineleukemia.org
Subject: Re: [Felvtalk] ELISA & IFA

okay, well, no one really wants to hear THIS one, but yes, using serum makes
the odds that an ELISA is accurate MUCH MUCH higher. in fact, as recently as
last november, a famous felv researcher (intials np) stated in a private
note to someone other than myself that an ELISA done on whole blood is
essentially useless. gee, great, this is at the same time that other
"professionals' are trying to assure us that standard,
done-at-the-vet's-office ELISA's (almost ALWAYS done with whole blood) are
highly accurate. i just found out about this about a month ago, and still
haven't digested it and what it means when the real experts (as opposed to
those who just have chosen ignorance) can't agree.

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