A retrospective review of cats with suspected false positive results in point-of-care feline leukemia virus tests and concurrent immune-mediated anemia

Objective: To describe clinical findings, diagnosis, treatment, and survival in 18 cats with anemia of suspected immune-mediated origin (ASIMO) and conflicting results using FeLV diagnosis tests, and to suggest an accurate way to assess their FeLV diagnosis. Animals: 18 cats. Procedures: Medical records from 5 veterinary institutions were retrospectively reviewed to identify cats with ASIMO, positive results on p27 SNAP ELISA, and negative results on pro-virus PCR testing in peripheral blood, in the absence of other identified triggers. Follow-up was recorded from diagnosis to the time of writing, and survival analysis was performed to assess similarities with previous published data. Results: 18 cats were enrolled from referral centers in Spain, Italy, and the United Kingdom. Both peripheral immune-mediated hemolytic anemia (IMHA; 12/18) and precursor targeted immune-mediated anemia (PIMA; 6/18) were described. When the SNAP ELISA test was rechecked in patients with disease control, SNAP ELISA positive results had become negative. Two cats had a relapse of the ASIMO, and the FeLV SNAP ELISA tested positive again. Other signs of FeLV disease did not appear in any of these patients despite immunosuppression. 14 cats (14/18 [78%]) were alive at the time of writing, and the mean estimated survival time was 769 days. Clinical relevance: This study describes incongruent FeLV results in cats with ASIMO. It supports the necessity to confirm FeLV SNAP ELISA positive results using additional tools, such as pro-virus PCR testing, as different p27 point-of-care and external serological tests may be inconsistent.