The FeLV Test: A Closer Look at Why Retesting is so Important for Your Cat's Future 🐾

Receiving a positive Feline Leukemia Virus (FeLV) test result for your beloved cat can be a terrifying moment. It’s natural to jump to the worst conclusion, but modern veterinary medicine offers a crucial piece of advice that can change your cat’s prognosis: A single positive test is not a final diagnosis.

The official guidelines from organizations like the American Association of Feline Practitioners (AAFP) emphasize that determining a cat's true infection status often requires more than one test performed at one point in time. For the sake of your cat, your family, and any other feline friends, understanding the testing process and the absolute necessity of retesting is one of the most important things you can do as a cat owner.

What is Feline Leukemia Virus (FeLV)?

FeLV is a serious, life-altering disease found in cats worldwide. It is a complex virus that primarily attacks the immune system, leaving cats vulnerable to a variety of secondary illnesses, blood disorders, and cancers.

FeLV is highly contagious and is spread through close, prolonged contact, commonly via saliva, nasal secretions, milk, urine, and feces. For most cats, this means transmission happens through mutual grooming, sharing food/water bowls, or bite wounds. Kittens are at the highest risk of becoming permanently infected.

Because of the severe consequences of FeLV, identification and segregation of infected cats are considered the most important measures for controlling the virus. This is why testing is so vital—it’s the cornerstone of prevention and management.

Level 1: The Initial Screening Test (The SNAP Test)

When you take your cat to the vet, the first test performed is usually a Point-of-Care (POC) test, often referred to by a brand name like a SNAP test. These simple, fast, in-clinic tests detect the presence of the FeLV p27 antigen.

The p27 antigen is a protein from the core of the FeLV virus itself. If this protein is detected in your cat's blood, it means viral particles are circulating, a condition called antigenemia (which usually means the cat is actively shedding the virus and is infectious).

The Risk of a "False Positive"

While these screening tests are designed to be highly sensitive and reliable, they are not infallible. Crucially, a positive result on a screening test—especially one in an otherwise low-risk, healthy, indoor cat—has a higher likelihood of being a false positive.

A false-positive result means the test came out positive, but your cat is not actually infected. This can happen due to minor technical issues or errors. Because the consequences of a positive FeLV diagnosis are so significant for a cat's future—including permanent segregation and life-long monitoring—additional confirmatory testing is strongly recommended. Never make a life-altering decision for your cat based on a single screening test result. The estimated number of false positive FeLV screening test results annually in the US is around 46,500!

Why Retesting is a Game-Changer: The Regressive Outcome

The main reason your veterinarian won't panic after a single positive SNAP test is that they know an initial infection can follow one of three pathways, and two of them lead to a much better prognosis:

1. Progressive Infection: This is the worst outcome. The cat's immune system fails to contain the virus, which infects the bone marrow and continually replicates and sheds. These cats are permanently infectious, have a shorter survival time, and typically succumb to FeLV-associated diseases.

2. Abortive Infection: The cat's immune system effectively eliminates the virus early on. The cat is deemed uninfected.

3. Regressive Infection (The Crucial Pathway): This is where retesting is essential. In this scenario, the cat's powerful immune response manages to contain, but not entirely eliminate, the virus. The cat’s body clears the circulating virus from the blood, so the cat is no longer shedding infectious virus and is SNAP test negative. These cats are at a low risk of developing FeLV-associated diseases and have a much better prognosis.

If your cat recently tested positive, they may be in the early, transient phase of a regressive infection. They could still have a positive antigen test for a short time before their body successfully suppresses the virus. Waiting and retesting is the only way to know if they will clear the infection from their bloodstream.

Level 2: The Power of PCR (Polymerase Chain Reaction)

When a cat tests positive on a screening test, the next step is often to send a sample to a referral laboratory for what is called Level 2 diagnostics. This step is vital to confirm the cat's true status and differentiate between a persistent progressive infection and a contained regressive infection.

The gold standard confirmatory test for this purpose is the Polymerase Chain Reaction (PCR) test, which looks for proviral DNA.

The Advantage of PCR: Looking for the Blueprint

• Looking Deeper: The SNAP test looks for the actual p27 antigen protein floating in the blood. The PCR test, by contrast, looks for the proviral DNA—the genetic blueprint of the virus that has been incorporated into the cat's own cellular DNA.

• Confirming Integration: FeLV is a retrovirus, meaning it integrates its genetic material (provirus) into the cat's genome. This is how a cat with a regressive infection can still have FeLV material present in their cells (proviral DNA positive), even if they are no longer actively shedding and are antigen-negative (SNAP negative).

• Clarifying the Status: By combining the results of the SNAP test (antigen in the blood) and the PCR test (proviral DNA in the cells), the veterinarian can classify the infection:

  • SNAP Positive + PCR Positive (Persistent Antigenemia): Confirms a high likelihood of a progressive, actively infectious cat.

  • SNAP Negative + PCR Positive: Indicates a successful transition to a regressive infection, where the cat is safe to live a near-normal life and is not shedding the virus.

In short, the PCR test provides the deep, molecular evidence needed to give a definitive diagnosis, moving beyond the preliminary screening of the SNAP test.

The Mandatory Retesting Protocol

If your cat has a positive POC/SNAP result, do not despair. Your veterinarian will likely follow a protocol that involves:

1. Immediate Confirmatory Testing: Sending a sample for a microwell ELISA or a PCR test immediately after the initial positive POC result.

2. Quarantine: Keeping the potentially positive cat away from all other cats in the home until their status is clarified.

3. The Wait and See: The cat will be retested with the POC test (and possibly PCR) 30 days after the initial positive test. This allows enough time for the cat’s body to mount an immune response and either clear the transient virus or permanently contain it (regressive outcome).

   
   

By embracing the need for retesting and relying on advanced diagnostics, such as PCR, you ensure

your cat is not subjected to an incorrect and devastating diagnosis. For cats, a positive FeLV test is not a death sentence; it’s a call for careful, mandatory retesting to determine their true path forward.

What makes CatDX.com different? We let you skip the vet and test for FeLV using saliva, not blood. Our tests are PCR-based is done in our laboratory. Read more below:

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