Diagnostic performances of two rapid tests for detection of feline leukemia virus antigen in sera of experimentally feline leukemia virus-infected cats

OBJECTIVES: The objective of this study was to compare the diagnostic sensitivities and specificities of WITNESS FeLV-FIV (Zoetis) and SNAP FIV/FeLV Combo Test (IDEXX) for the detection of FeLV p27 antigen in the sera of experimentally feline leukemia virus (FeLV)-infected cats. METHODS: Diagnostic sensitivities of WITNESS and SNAP were determined through testing of 47 serum samples collected from cats day 56 post-experimental infection with a virulent FeLV Rickard strain. Successful experimental infection was confirmed based on observation of FeLV antigen and proviral DNA in anti-coagulated (EDTA) whole-blood samples by immunofluorescent antibody (IFA) test and PCR, respectively. Diagnostic specificities of both tests were determined through testing of sera of 92 laboratory-housed, non-FeLV-exposed specific pathogen-free (SPF) cats. RESULTS: Forty-one of 47 blood samples were IFA positive, whereas all 47 samples were PCR positive. All 92 non-FeLV-infected SPF cats were IFA and PCR negative. In comparison to IFA as the reference method, both WITNESS and SNAP tests yielded equivalent sensitivities and specificities of 100% and 97.8%, respectively. In comparison to PCR as the reference method, both WITNESS and SNAP tests likewise performed equivalently, with sensitivities and specificities of 91.5% and 100%, respectively. CONCLUSIONS AND RELEVANCE: Sensitivity and specificity of WITNESS FeLV-FIV for identifying FeLV p27 antigen in the sera of these experimentally FeLV-infected and non-FeLV-exposed SPF cats equaled those of the SNAP FIV/FeLV Combo Test. However, all positive results, regardless of the point-of-care test used, should be confirmed before making clinical decisions such as segregation from other cats or euthanasia.