Understanding the Rivalta Test for FIP Screening

The Rivalta test is most commonly used in cats to evaluate effusion (abdominal or pleural fluid). You mix distilled water (8 mls) with a drop of acetic acid or vinegar (10 drops), then gently add a drop of the effusion.

Sensitivity: 91.3% | Specificity: 65.5%

Positive Test

The drop keeps its shape, or looks like a jellyfish/cloud.

Suggests: A high protein, inflammatory effusion (classically seen with FIP).

Negative Test

The drop disperses and disappears into the solution.

Suggests: More consistent with a transudate or non-inflammatory fluid.

Why It Matters

It’s not a definitive test, but it’s a helpful screening tool when you’re building your case. A positive Rivalta increases suspicion for FIP, especially when paired with signalment, clinical signs, and other diagnostics.