Which statement best describes the diagnostic approach to suspected FIP in cats?

• A. FIP diagnosis is challenging; supportive tests like Rivalta test and coronavirus PCR or immunohistochemistry are often used, with histopathology providing definitive confirmation.
• B. FIP is easily diagnosed with a single blood test.
• C. FIP can be confirmed with imaging alone.
• D. FIP cannot be diagnosed reliably and is treated empirically.

Answer: (A)

FIP is notoriously hard to confirm with a single test, so the best approach is to use a combination of supportive assessments and tissue analysis. In practice, signs and routine tests raise suspicion, but a definitive diagnosis comes from testing that directly detects the virus in affected tissue or fluid. The Rivalta test on effusion can be supportive, while coronavirus PCR on effusion, blood, or tissues helps detect viral RNA. Immunohistochemistry can demonstrate FCoV antigen within Lesions, and histopathology showing the characteristic inflammatory pattern confirms the diagnosis, though tissue samples are often needed and may require biopsy or occur at necropsy. Imaging and routine blood work can support suspicion but don’t confirm FIP on their own, and treating empirically without confirmation isn’t reliable.