Answer: Currently, there are three tests available which can be perfumed by certain laboratories (possibly even your vet’s own practice laboratory) on a small blood sample collected from your cat. These are virus isolation tests, an immunofluorescent tests, and an immunosorbent assay (‘Leukassay’).
In interpretation of results depends on which tests is used. Using more then one can provide valuable confirmatory evidence. In general it is advisable to repeat the test three months later. This is because some cats which at first give a negative result may be in the incubation stage of the disease and will later show positive, and some cats appearing positive initially may recover (i.e. get rid of the virus) and then give a negative reading.
Furthermore, not ever cat with lymph sarcomas does have other causes.
