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Choosing and Interpreting In-House FIV/FeLV Combo Tests

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    Feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) are contagious retroviruses that can cause serious illness in cats.

    Infected cats may develop bone marrow suppression, chronic inflammatory conditions, and cancer (especially lymphoma), and be more susceptible to other infectious diseases due to a weakened immune system.

    With all these health consequences, it’s no surprise that a retroviral infection may significantly shorten a cat’s lifespan.

    Prevention is key for limiting the prevalence of these diseases. Since these viruses are typically spread by close contact (mutual grooming, catfights, etc.), it’s important to identify and isolate infected cats, to prevent exposure and spread of the disease to other cats. 

    For all these reasons, the American Association of Feline Practitioners (AAFP) recommends testing for FIV and FeLV when a cat is first adopted, prior to initial vaccination against these diseases, after a potential exposure, and if clinical signs of retroviral infection develop.

    Which Tests are Available for FIV/FeLV Testing in Cats?

    Tests are available for in-house (point of care) use. Laboratory testing is also available, which includes a wider range of testing options and confirmatory testing.

    For point of care tests, here are two popular options for veterinary practices…

    • IDEXX SNAP FIV/FeLV Combo Test

    IDEXX claims to have high sensitivity and specificity, with reference lab quality technology. Results are available in 10 minutes, using 3 drops of sample. A SNAP Pro Analyzer is available to automatically activate and read tests, and add results to the medical record.

    • Zoetis WITNESS FeLV/FIV Rapid Test

    The WITNESS test is meant to be easy to use and affordable. It works with just 1 drop of sample, with results available in 10 minutes. The test offers room temperature storage, an extended (12-month) shelf life, and no need to snap the test.

    Zoetis also offers the VETSCAN FeLV/FIV Rapid Test, which appears to have very similar specifications to the WITNESS. One difference is that the VETSCAN test has a single test window, versus two separate test windows for the two diseases in the WITNESS test.

    Considerations for FIV/FeLV Testing

    To get the most accurate results, it’s best to use serum or plasma rather than whole blood. Although test instructions specify whole blood (and most of the time this works just fine), many experts note that occasionally, whole blood can result in a faint false positive. This is due to a protein or interference from red blood cells.

    It’s also important to note that the FeLV test is an antigen test, and the FIV test is an antibody test. Therefore, the FIV test may pick up on an antibody response from a vaccination rather than a natural infection. This may complicate testing in some cases, and it’s recommended to know a cat’s FIV status prior to vaccination.

    Additionally, in-house testing is often considered a screening test, in the sense that confirmatory testing is recommended for positive results. This commonly includes IFA testing for FeLV, and Western Blot testing for FIV.

    Purchasing Considerations

    Here are a few important considerations before making a purchase…

    • Brand preference. Maybe a veterinarian or their team has had good experience with a particular brand. Or, if the company has any additional equipment or tests (such as hematology or chem analyzers) the practice is also interested in, it might be possible to negotiate a better deal for everything together.

    • Contracts. It’s always important to check the contract closely when making a purchase, to see if there’s a minimum requirement of tests per month or any other stipulations.

    • Quantity sold and expiration dates. See if you’ll be able to use all the tests before they expire, or if the company will refund any unused tests. 

    • Available support. Is there a helpline for any technical questions or for help with confusing or inconsistent results? And does the company help with confirmatory testing, especially if in-house test results are inconsistent or don’t seem to line up with the cat’s history or symptoms?

    Details and specifics of these tests may evolve over time. It’s important to check directly with the company for the most up-to-date information before making a purchase.

    With all these factors in mind, see which option works best for the needs of your individual practice. 

    Written by: Dr. Tammy Powell, DVM