Diagnosing feline infectious peritonitis (FIP) is a complex task. The lack of specific clinical symptoms, especially in cases without effusion, makes it challenging. To diagnose FIP, a combination of medical history, symptoms, hematological examination, imaging studies, effusion analysis, and laboratory tests are required. It is crucial to understand the sensitivity, specificity, predictive values, likelihood ratios, and diagnostic accuracy of each diagnostic method to diagnose FIP correctly. The specificity of diagnostic tests is more important than sensitivity in highly fatal diseases like FIP, as it helps prevent the euthanasia of cats wrongly diagnosed with FIP.
Traditional infectious disease diagnostics involve detecting the presence of the pathogen. However, regular feline coronavirus PCR tests cannot differentiate between Feline Enteric Coronavirus (FECV) and Feline Infectious Peritonitis Virus (FIPV). Even if a positive result is obtained, it does not confirm the virus's association with the disease. Relying solely on mutation points still does not guarantee a 100% diagnosis, although further mutation analysis can confirm whether it's FECV or FIPV. Blood sample PCR results are usually not helpful for diagnosing FIP. The only definitive method to confirm FIP is by detecting the virus within the tissues (via antigen staining or RT-PCR), which requires collecting tissue pathology samples. Immunostaining for Feline Coronavirus (FCoV) antigen within macrophages in the lesion area is considered the gold standard for diagnosing FIP.
