The aim of this study was to provide a clinical and laboratory rationale for the comprehensive diagnosis of feline infectious peritonitis (FIP) in the context of domestic veterinary practice. The paper presents data from a survey of practicing veterinarians, evaluates the diagnostic value of routine blood and exudate parameters, describes the results of PCR-based diagnosis verification, and assesses the effectiveness of confirmatory diagnosis through trial treatment (ex juvantibus). The research methodology included a retrospective analysis of 3,294 laboratory samples tested for coronavirus at the Bald Laboratory (Kyiv), a survey of 41 practicing veterinarians from various regions of Ukraine (with a predominance of Kyiv-based specialists) regarding their FIP diagnostic algorithms, and a retrospective review of 85 confi rmed clinical cases of FIP (22 cats with the eff usive form and 63 animals with the non-eff usive or mixed form). Clinical case analysis covered medical history, complete blood count and biochemical blood parameters, effusion characteristics, PCR test results, and clinical response to antiviral therapy with GS-441524. The survey revealed that 97,5 % of veterinarians use the correct basic diagnostic panel; however, a diagnostic gap was identifi ed: 46.3% of specialists still order non-specific serum antibody tests, and 34,1 % rely on fecal antigen testing, which has no confirmatory value for FIP. Analysis of clinical cases showed that group housing is the primary risk factor, accounting for over 80 % of patients, and that disease onset most commonly occurs between 5 and 12 months of age. Jaundice with a marked elevation in bilirubin was recorded in 45,4 % of cases. The findings confi rm the high sensitivity of a reduced albumin-to-globulin ratio and the specifi city of eff u sion PCR in the positive cohort. In cases of the dry form, where tissue biopsy is frequently unavailable, the most justified approach is multimodal assessment combined with trial therapy. The results are consistent with current understanding of a comprehensive approach to FIP diagnosis. The use of GS-441524 as an ex juvantibus diagnostic tool demonstrates high practical applicability, particularly in the non-eff usive form of FIP, and supports initiating therapy before definitive results of complex tests are available. Implementation of a diagnostic algorithm emphasizing effusion PCR and early antiviral therapy is a promising strategy for improving in vivo FIP diagnosis in Ukraine.

Keywords: cats, feline infectious peritonitis, FIP, effusion, Rivalta test, polymerase chain reaction, mRNA, GS-441524, ex juvantibus diagnostics.