Research overview: the Rivalta test and effusion analysis in FIP

The Rivalta test, a simple inexpensive bedside test that observes whether a drop of effusion fluid retains its shape in a dilute acetic acid solution, has been studied as an aid to distinguishing FIP effusions, which are high in protein and inflammatory mediators, from other causes of fluid accumulation. While not definitive, it offers reasonable predictive value in appropriate populations and remains useful where advanced testing is unavailable. This overview synthesizes the effusion-diagnostic literature rather than a single source, describing the biochemical basis of the test, its sensitivity and specificity limitations, and how it fits within a broader diagnostic workup that includes cell counts, protein measurement, and confirmatory testing when committing a cat to antiviral therapy.