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Why Shelters Are Moving Away From Combo Testing Cats

Author: Dr. Keri Morgan, Metro East Humane Society's Medical Director Each year, more and more cats enter animal shelters, which puts a strain on already limited resources. The ever-changing landscape of shelter medicine requires that we constantly examine and update our policies to best reflect the needs of our animals. In the past, most shelters tested every cat for FeLV and FIV—two viruses that affect a cat’s immune system. This test is called a “combo test.” Additionally, the American Association of Feline Practitioners (AAFP) suggests that veterinarians screen all cats for FeLV and FIV at least once. So why, then, are many shelters moving away from combo testing all of their healthy cats? Let’s take a closer look.

What are FeLV and FIV?

FeLV and FIV are both categorized as retroviruses, meaning they use RNA (instead of DNA) to infect the body. They spread through saliva, mom to kittens, and deep bite wounds. After infection, the RNA converts itself back into DNA and continues to replicate and cause illness in the host.

Feline Leukemia Virus (FeLV) has no cure, and the virus weakens the immune system. Over time, this can also cause anemia, secondary infections, weight loss, oral disease, and cancer. Some cats may carry the virus without showing symptoms for years, while others may develop progressive disease more quickly. Likewise, Feline Immunodeficiency Virus (FIV) also has no cure and targets the immune system. FIV is similar to the human HIV virus but is species-specific and cannot be passed to humans. Many cats with FIV can live for years without showing symptoms, but as the disease progresses, they may experience recurring infections, weight loss, poor coat condition, and cancer. The progression of FIV, especially compared to FeLV, is often slow, and many infected cats can live a relatively normal life with proper care. New research suggests that the chances of disease spread between cats are relatively low, especially under ideal circumstances, which we will discuss later.

No test is perfect.

  1. False Positives

While we rely on our diagnostic tests and tools when caring for our patients, NO TEST provides 100% accurate results. FeLV/FIV tests, in particular, have less accuracy than some of our other tests, and this is because of the complex nature of the retroviruses. Less than 3% of all cats nationwide are truly positive for FeLV. When you crunch the numbers, if a shelter were to test every healthy cat for FeLV, 36% of our positive results would be inaccurate. In other words, one-third of our cats with a positive test result for FeLV would actually NOT have the disease! Mislabeling a cat as FeLV positive can put them at risk for increased length of stay in the shelter and even unnecessary euthanasia.


  1. False Negatives

Let’s look at these tests from one more angle. Cats who have been infected with FeLV or FIV may not test positive right away. A cat who is infected with FeLV takes 30 days before a combo test can detect a positive result, and a cat with FIV takes at least 60 days. Thus, a “negative” test result can lead to a false sense of security, especially when routinely testing all healthy cats immediately upon intake.


When SHOULD we combo test cats?

  1. Sick Cats

This answer will be different for every shelter, depending on the resources available to them. Not only are combo tests quite costly, but the amount of time it takes for a staff member to appropriately restrain a cat, draw blood, and run the test is high - it adds up! However, combo tests are an extremely valuable tool, especially when utilized for sick or injured cats. Circle back to the symptoms of FeLV and FIV: anemia, bacterial infections, dental disease, and cancer. If a cat comes to our shelter with an abscess, dental disease, and/or appears overall unthrifty, they are more likely to truly have FeLV and/or FIV. In these cases, a positive test result is more likely to be accurate. Shelters should also consider the history of the cat. For example, cats rescued from a hoarding situation would be at higher risk due to the high stress of their environment and constant, close proximity to other cats. Additionally, cats presenting with a bite wound have a known potential exposure to FIV.


  1. Group Housing

Shelters often utilize group housing for cats. Not only does this save space, but many cats prefer to be housed in a group setting, which allows for more enrichment and lower stress levels while waiting for their adoptive home. The decision to combo test cats in group housing again depends on the shelter’s available resources. Healthy cats that are spayed/neutered and housed in low-stress environments are very unlikely to transmit FeLV or FIV to other cats. A low-stress environment for group-housed cats includes abundant space, multiple food and water sources, and multiple litter boxes. Therefore, it is not unreasonable to forgo combo testing for cats that are appropriately group housed.

Wrapping It Up

Combo testing is an important  tool for veterinarians, and the AAFP recognizes the importance of screening for FeLV and FIV in all cats. However, for shelters managing large numbers of healthy cats, routine combo testing may not be the best use of time, money, or staff resources. At Metro East Humane Society, we encourage all of our adopters to establish a strong relationship with a primary veterinarian when they welcome a new animal into their home. Your veterinarian will help guide you on what is best for you and your new cat!


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