The Rivalta Test
The Rivalta Test was developed by Fabio Rivalta as a means to differentiate a transudate from an exudate. It is a simple, inexpensive method that produces an immediate result, and does not require special laboratory equipment. Only distilled water and either acetic acid or distilled vinegar is needed, along with a small sample of the effusion fluid.
The Rivalta test relies on the formation of a precipitate when a fluid sample from an effusion is added to acetic acid.
Studies have shown the Rivalta test has a sensitivity of 91-98% and a specificity of 66-80% for diagnosing FIP in cats.
Performing the Rivalta Test
To perform this test, a transparent test tube (volume 10 ml) is filled with approximately 7–8 mL of distilled water to which any one of the following is added:
one drop (20–30 μL) of acetic acid (98–100%)
OR 2-3 drops 25% white vinegar
OR 10 drops of 5% white vinegar
and mixed thoroughly.
On the surface of this solution, 1 drop of the effusion fluid is carefully layered. If the drop disappears and the solution remains clear, the Rivalta's test is defined as negative. If the drop retains its shape, stays attached to the surface or slowly floats down to the bottom of the tube (drop- or jelly-fish-like), the Rivalta's test is defined as positive.