Neither FeLV nor FIV are an immediate death sentence, but both mean that your cat has a weakened immune system and is at higher risk for other infections. Both can be transmitted to other cats (FLV through close contact such as mutual grooming or sharing water dishes; FIV can only be transmitted through bite wounds or sexual contact), and so contagion is a concern in a multi-cat household or if your cat goes outdoors. In cats with no symptoms, a positive diagnosis lets you know that your cat should be kept indoors and that you need to monitor his or her health especially closely, to catch any symptoms early. In the case of FeLV, other uninfected cats in the household should be vaccinated or separated from the infected cat. In cats who test positive when they are ill, the diagnosis will allow you and the vet to make informed decisions about your cat's treatment and quality of life.