This cat has tested positive for FeLV or feline leukemia virus. This is a retrovirus that alters the immune system of the cat making it more susceptible to illness. FeLV can cause cats to have a shorter lifespan. If the cat tested positive and was less than 4-6 months old, there is a chance that the virus may clear. This is what we call a regressive case. This means that the body has done a good enough job to cause your cat to become negative. This can only be confirmed by retesting serially over the next 6-12 months. Another form of the virus is what is called the dormant form. This can occur at any point and happens when the virus becomes dormant and suppressed by the immune system, causing the tests to be negative and the cat to be subclinical. At any point, if this is the case that we are dealing with, the cat may experience acute sickness due to the ability of the virus to become active later in life. The most common form is progressive in which the cat experiences more health problems over the coming months to years. Typically, cats experience this form of FeLV and do not make it past around 2-3 years of age. The 2-3 years is a median survival time which means the cat can live longer or shorter than that period of time. Typically, these cats do not die on their own and require euthanasia at some point to relieve suffering. It is impossible for us to know which form your cat has at this time. If your cat is an adult (older than 3 years old), it is more likely that it has the dormant form, because progressive form cats do not typically survive past 2-3 years of age.
We recommend you follow up with your regular veterinarian and mention that this cat has FeLV. That way, you can get on a good monitoring schedule.