Feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV) both belong to the same group of viruses, the retrovirus group. This means they are somewhat related to one another and act in a similar way.
Retroviruses such as FeLV and FIV are particularly successful because the immune system usually fails to remove them completely (unlike many other viruses), so affected cats become infected for life. Feline immunodeficiency virus (FIV) is related to the human immunodeficiency virus (HIV), however humans and cats cannot infect each other with their respective viruses.
There are two possible situations in which tests are carried out for either FeLV or FIV.
Whatever the reason for testing a cat, it is usually possible to diagnose FeLV and FIV with a blood test that can be done at the practice. However, in some cases we may suggest sending a blood sample to a laboratory for more advanced testing methods to be used.