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Feline Leukemia Test

Feline Leukemia Test

by Michael
(London, UK)

Assure FeLV Feline Leukemia Virus Antigen Test Kit

“Feline leukemia test” is a search term on the internet so people clearly want to know about it. The source of the information below comes from a book I use frequently for good reason, Cat Owner’s Home Veterinary Handbook by Drs Carlson DVM and Giffin MD. It was published in 1995 so I have checked other sources to see if these tests have been modernised. They are the same as at 2010.

There are two tests available:

  1. IFA Test (immunofluorescent antibody test4) – this feline leukemia test is conducted by a “reference” laboratory. I couldn’t find a definition to the phrase “reference laboratory” but the it must mean a laboratory that test and checks with “reference” to known indicators etc. In this case the lab detects virus antigen in infected white cells. The results take about 1-2 days to come through from the laboratory. Some definitions: White cells: White blood cells (WBCs), or leukocytes are cells of the immune system defending the body against both infectious disease and foreign materials. Virus: A virus is a small infectious agent that can replicate only inside the living cells of organisms. Antigen: A molecule recognized by the immune system1.  If positive it indicates that the bone marrow is infected. This is turn means that there is a high probably that the cat is viremic and shedding the virus in saliva and is infective to cats. Definition: Viremic: a condition in which virus particles circulate and reproduce in the bloodstream2.  Apparently 97% of cats tested positive in the IFA feline leukemia test remain viremic and the virus is never eliminated. The IFA test is less sensitive than the ELISA test3. Test sensitivity is good3.
  2. ELISA test (enzyme linked immunsorbent assay4) – this feline leukemia test detects virus antigen in whole blood, sperm, saliva and tears. A test kit is available for home and clinic use. The test takes about 10-20 minutes to perform. This test is more likely, the doctors say to detect “weak, early or transient infections”. Test sensitivity is very good3but less good on saliva and tears. I could not find a supplier of the home test kit on the internet when searching for 10 mins but found one after about 20 mins searching! (see the header picture).  It is available from Amazon and is called the Assure FeLv Feline Leukemia Virus Antigen Test Kit 25 tests. It cost $259.99! It tests the cat’s saliva. It appears not to be available anywhere other than the USA. If the test is positive the cat may have a transient viremia. This may indicate the early stages of the disease or the cat may recover completely. A follow up IFA test is recommended by the Drs. and it will also confirm, if positive, that the cat is shedding and liable to infect other cats. Both the ELISA and IFA tests should be repeated (8-12 weeks later) to see if the virus has been eliminated and/or if the cat has become positive after 12 weeks having been found negative earlier.

The more common feline leukemia test is the ELISA test. Both these tests will test negative for a latent infection. The test for a latent infection has to be carried out on bone marrow in which the dormant virus might be present.

If the ELISA is positive but the IFA test is negative, a retest is required  in 60 days and thereafter annually until test results agree5.


1. Wikipedia authors

2. Free Dictionary




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Michael Broad

Hi, I'm a 71-year-old retired solicitor (attorney in the US). Before qualifying I worked in a many jobs including professional photography. I have a girlfriend, Michelle. I love nature, cats and all animals. I am concerned about their welfare.

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