• All cats should be tested for infection with FeLV and FIV.
• Cats infected with FeLV or FIV may live for many years, so decision for euthanasia should never be made solely on the basis of retroviral infection.
• Confirmed positive test results are only an indication of retrovirus infection, not clinical disease. Diseases in cats infected with FeLV or FIV may not be the result of retrovirus infection.

• The preferred initial tests are for soluble antigen. Most cats will have positive results within 28 d after exposure; however, the time between exposure and development of antigenemia is extremely variable and may be considerably longer.
• IFA tests detect cell-associated antigen and are the preferred confirmatory tests.
• PCR-based assays that detect viral RNA or DNA offer a promising approach to confirmatory FeLV testing.

• Positive free-antigen tests may reflect transient or persistent viremia.
• Positive tests for bone marrow infection (IFA) are highly likely to represent persistent viremia.
• Discordancy may be a consequence of stage of infection, variability of host response, or technical problems with the test.
• If results of 2 soluble antigen tests are discordant, an IFA test should be performed immediately.
• If a soluble antigen test is positive and an IFA test is negative, both tests should be performed again in 60 d and then annually until results are in agreement. True infection status is difficult to determine when discordancy persists, but these cats should be considered potential sources of infection for other cats.
• Maternally derived antibodies do not influence results, so kittens may be tested at any age, although infection in newborn kittens may not be detected for weeks to months after birth.
• FeLV vaccination does not affect test results for FIV.

• Currently available FIV tests (immunochromatic, WB, IFA) detect FIV antibodies. Most cats develop FIV antibodies to FIV within 60 d after infection. However, the time for sero-conversion is variable and may be longer.
• Immunochromatic tests are the preferred screening tests. All positive screening test results should be confirmed by WB or IFA.
• PCR-based assays that detect viral RNA or DNA offer poor sensitivity due to the marked variability of the viral genome.

• There is a high correlation between the detection of antibodies and persistent infection or vaccination.
• If a screening test is positive and an IFA test is negative, both tests should be performed again in 60 d and then annually until results of both tests are in agreement. True infection status is difficult to determine when discordancy persists, but these cats should be considered potential sources of infection for other cats.
• Use of whole-virus vaccines against FIV results in false-positive FIV test results.
• Maternally derived FIV antibodies in kittens < 6 mo old confound interpretation of positive test results. Kittens born to infected queens may test positive for antibody, yet most are not infected. Kittens should be retested at 60-d intervals. If test results performed > 6 mo of age are still confirmed positive, these kittens are considered infected.

Reference: Levy. Proc. ACVIM Forum, 2004; Uhl, Heaton-Jones, et al. Vet Immunol Immunopathol 90:113-132, 2002; Kahler. JAVMA 221:1231-1234, 2002; Levy, Richards, et al. Comp Cont Edu Pract Vet 23:652-657, 692, 2001.