Question of the Day

Perform the Rivalta test to help distinguish feline infectious peritonitis (FIP) from other causes of peritoneal effusion. Mix 8 mL distilled water with a drop of 98% acetic acid in a clear tube. Carefully layer a drop of effusion on top.

If the effusion dissolves in solution, the result is negative; if the effusion remains as a drop or ball, or does not dissolve, the result is positive. The Rivalta test is best at ruling out FIP; a negative test means FIP is very unlikely. A positive Rivalta test requires confirmation with other tests for FIP.

Biopsy with immunohistochemical staining for FCoV antigen or FCoV RT-PCR assays are more sensitive and specific than the Rivalta test but need to be sent to the lab so results take longer.

Click here to see an image of the Rivalta test. The effusion in this image contains new methylene blue to improve clarity. For more information about FIP Dx and Tx, check out this article from the European Advisory Board on Cat Diseases.

Images courtesy of Dr Kalumet (peritoneal fluid, Rivalta test).