The Rivalta test has been used routinely in Europe to diagnose feline infectious peritonitis (FIP) in cats with effusions, but its diagnostic accuracy is uncertain.
The objectives of this study were to calculate sensitivity, specificity, and positive (PPV) and negative (NPV) predictive values of the Rivalta test for FIP and to identify correlations between a positive Rivalta test and variables measured in effusion fluid and peripheral blood.
In this retrospective study, medical records of cats with effusions were reviewed, and cats with conclusive results for the Rivalta test were included. The prevalence of FIP in this population was determined, and sensitivity, specificity, and PPV and NPV of the Rivalta test were calculated. Variables measured in effusion fluid and peripheral blood were compared between cats that had positive or negative Rivalta tests using the Mann–Whitney U-test and multivariate analysis.
Of 851 cats with effusions, 782 had conclusively positive or negative results for the Rivalta test. A definitive final diagnosis was made in 497 of these cats. Prevalence of FIP in cats with effusion and a conclusive Rivalta test result was 34.6%. The Rivalta test had a sensitivity of 91.3%, specificity of 65.5%, PPV of 58.4%, and NPV of 93.4% for the diagnosis of FIP. These values increased when cats with lymphoma or bacterial infections were excluded, or when only cats ≤ 2 years were considered. Increased effusion cholesterol concentration and specific gravity as well as decreased serum albumin:globulin ratio and hyperbilirubinemia were positively correlated with positive Rivalta test results.
Sensitivity, specificity, and PPV of the Rivalta test for the diagnosis of FIP were lower than previously reported except when used in young cats. The components in effusions that lead to a positive Rivalta test remain unknown, but the positivity is not simply related to high total protein concentration.