Which statement best describes the diagnostic approach to suspected FIP?

• A. Definitive confirmation can be achieved with a single blood test.
• B. Definitive confirmation often requires histopathology, with supportive tests aiding suspicion.
• C. Imaging alone confirms FIP.
• D. FIP cannot be diagnosed and must be treated empirically.

Answer: (B)

Diagnosing FIP hinges on tissue-level evidence rather than a single blood test. The most definitive way to confirm FIP is histopathology of affected tissues, which reveals the characteristic pyogranulomatous vasculitis and inflammatory lesions, often supported by immunohistochemistry showing FCoV antigen in the lesions. Supportive tests help build a case for suspicion—such as analysis of effusions (in the wet form, the effusion is typically high in protein with variable cellularity and may yield a positive Rivalta test), hematology and biochemistry trends, and molecular tests like RT-PCR for FCoV on effusion or other samples—but these alone do not provide a definitive diagnosis. Imaging can suggest organ involvement or effusions but cannot confirm FIP by itself. Therefore, the best approach is that definitive confirmation often requires histopathology, with supportive tests aiding suspicion.