A combo test for cats is a simple blood test that screens for two serious viral infections at once: feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV). It’s one of the most common screening tests in veterinary medicine, typically run right in the clinic with results available in minutes. If you’re adopting a cat, bringing home a stray, or your vet has recommended one, here’s what the test involves and what the results mean.
What the Test Actually Detects
The “combo” name comes from the fact that a single test kit checks for two different viruses using two different methods. For FeLV, the test looks for a specific viral protein (called p27) circulating in the cat’s blood. This is a direct marker, meaning the test is searching for pieces of the virus itself. For FIV, the test works differently: it detects antibodies the cat’s immune system has produced in response to infection, not the virus directly.
This distinction matters because it affects how results are interpreted, especially in certain situations like kittens or previously vaccinated cats.
Why These Two Viruses Matter
FeLV and FIV are both retroviruses that suppress a cat’s immune system over time, making them vulnerable to secondary infections, cancers, and chronic illness. FeLV spreads through prolonged close contact, shared food bowls, and grooming, and is especially common among cats that live in close quarters. FIV spreads primarily through deep bite wounds, which is why it’s most prevalent in unneutered male cats that fight. Both viruses can be carried silently for months or years before a cat shows any symptoms, which is why screening is so important.
When Your Cat Should Be Tested
The American Association of Feline Practitioners (AAFP) recommends testing in several specific situations:
- When you first get a cat or kitten, regardless of where they came from
- Before vaccinating against FeLV or FIV
- After potential exposure to an infected cat or a cat whose status is unknown
- When a cat is sick, particularly with oral disease, abscesses, or respiratory infections
Cats with outdoor access, intact males, and cats from hoarding situations or shelters are at higher risk. Shelters typically screen cats before adoption when resources allow, prioritizing sick cats or those with bite wounds when testing every animal isn’t feasible.
For breeding catteries, the guidelines are stricter. All cats should be tested initially, then retested no sooner than 60 days later to catch infections that were too recent to detect the first time. Any cat brought in from outside should be isolated and tested on arrival, with a follow-up test 60 days later before mixing with other cats.
How the Test Works
The most widely used version is a lateral flow ELISA test, a small cartridge that works similarly to a home pregnancy test. Your vet draws a small blood sample (about 1 ml of whole blood, serum, or plasma), applies it to the test device, and reads the results based on colored dots or lines that appear. In-clinic tests typically produce results within about 10 minutes. If the sample is sent to an outside lab, turnaround is closer to two business days.
The test costs roughly $40 to $50 at most clinics, though prices vary by location. Some shelters and low-cost clinics offer it for less.
How Accurate Are the Results?
Point-of-care combo tests are generally very reliable, but accuracy varies between brands. In a study comparing four common test kits, the IDEXX SNAP test performed best, with 100% sensitivity and 100% specificity for FeLV and 97.9% sensitivity with 99.0% specificity for FIV. Other brands ranged from about 86% to 92% sensitivity for FeLV and 92% to 97% for FIV.
In practical terms, a negative result on a high-quality test is very trustworthy. A positive result is also likely accurate, but vets generally recommend confirming a positive with a second method, especially if the cat appears healthy or the result is unexpected. Confirmatory options include PCR testing, which detects the virus’s genetic material directly, or a specialized lab-based test called IFA for FeLV.
Why Kittens Need Retesting
Kittens born to FIV-positive mothers can carry their mother’s antibodies for several months after birth. Since the combo test detects FIV by looking for antibodies, a kitten may test positive even if it isn’t actually infected. These maternal antibodies gradually fade, so a kitten that tests positive for FIV should be retested after about six months of age. A positive FeLV result in a kitten is more straightforward since that side of the test detects the virus itself, but retesting at least 60 days later is still recommended to confirm the result.
FIV Vaccination Can Cause False Positives
An FIV vaccine was available in some countries for years (it has since been discontinued in many markets), and cats that received it pose a testing challenge. Because the vaccine teaches the immune system to produce antibodies against FIV, vaccinated cats will test positive on antibody-based combo tests even though they aren’t infected.
Research shows that the SNAP Combo test detected antibodies in 100% of vaccinated, uninfected cats for at least 34 weeks after vaccination, and potentially for years. Some newer test kits that detect a narrower set of antibodies can distinguish vaccinated cats from truly infected ones. In one study, the Witness and Anigen Rapid tests correctly returned negative results in 100% of vaccinated, uninfected cats when tested six months or more after vaccination, while the SNAP Combo continued to read positive. If you’ve adopted a cat with an unknown vaccination history and it tests FIV-positive, PCR testing can confirm whether the virus is actually present.
What a Positive Result Means for Your Cat
A positive combo test is not a death sentence. Cats with FeLV or FIV can live for years, sometimes with relatively few health problems, especially with good nutrition, regular veterinary care, and an indoor-only lifestyle that reduces stress and exposure to other illnesses. FIV-positive cats in particular often have a near-normal lifespan.
The main practical changes involve keeping positive cats indoors to prevent spreading the virus to other cats and monitoring them more closely for signs of illness. FeLV-positive cats should ideally be housed separately from uninfected cats, since the virus spreads through casual contact. FIV-positive cats pose less risk to housemates since transmission requires bite wounds, but separation is still recommended when possible.