Report of Three Feline Infectious Peritonitis (FIP) Cases with Negative Rivalta Test: Diagnostic Challenges in Confirming a Definite Diagnosis

Background: Feline infectious peritonitis (FIP) is a fatal, immune-mediated disease of cats caused by feline coronavirus (FCoV). The Rivalta test has conventionally been employed as an easy and quick screening method to differentiate FIP effusions from other causes of exudation. However, false negativity may give rise to diagnostic dilemmas. The present report describes three uncommon cases of FIP with negative Rivalta tests and emphasizes that diagnosis relies on integration of multiple diagnostic approaches. Methods: Three Persian cats, two males and one female, aged ۶ months to ۲ years, were presented with progressive lethargy, anorexia, and fluctuating fever. Abdominal distension was observed in all cases. Abdominocentesis resulted in clear to straw-colored effusions that were negative on the Rivalta test. Routine hematology demonstrated non-regenerative anemia, lymphopenia, and hyperglobulinemia with depressed albumin-to-globulin ratios (<۰.۶). Hyperechoic mesenteric fat, mild hepatomegaly, and enlarged mesenteric lymph nodes were detected through abdominal ultrasonography. Results: Cytological examination of effusions revealed high-protein, moderately cellular samples containing macrophages and degenerated neutrophils within a proteinaceous background. RT-PCR performed on the effusion detected FCoV RNA in all three cats, confirming a diagnosis of FIP. Two cats received symptomatic treatment with corticosteroids and supportive therapy but died within two weeks. One cat received adjunctive antiviral therapy (GS-۴۴۱۵۲۴) and showed marked clinical improvement during a two-month follow-up. These cases illustrate the potential for false-negative Rivalta tests in FIP, especially in the early or atypical disease stages. Conclusion: This case series evidences that a negative Rivalta test does not rule out FIP. The diagnosis of FIP requires integration between clinical, biochemical, and imaging findings with molecular data. Clinicians should use Rivalta results guardedly, particularly when clinical and laboratory findings are supportive of FIP. Advanced molecular tests, such as RT-PCR, have added confirmation value in equivocal cases and may significantly enhance case management and prognosis assessment.

کلیدواژه ها:

Cat ، FIP ، Rivalta test ، RT-PCR ، Effusion ، Diagnosis ، Case series