This article is from the Feline Leukemia (Cats) FAQ, posted to rec.pets.cats newsgroup. Maintained by Erin Miller with numerous contributions by others.
Yes. If you have a cat which tests positive on the ELISA test, you should immediately have an IFA test done. If it tests negative on the IFA test, you should have your cat retested with the ELISA test in 3 months. If a cat does not test negative again in roughly three months, chances are it will always test positive. Vets and virologists have devised an entire classification scheme of the different types of infected cats (transiently infected, persistently infected, etc.) based on the ELISA and IFA tests. It can be very confusing and if you are interested in learning the details you should consult with your vet regarding your particular cat's status.