Performances of different diagnostic tests for feline infectious peritonitis in challenging clinical cases

Feline infectious peritonitis (FIP) can be difficult to diagnose. Histopathology is considered the gold standard test but immunohistochemistry (IHC) is mandatory to confirm/exclude the disease. This study aimed to assess the performances of tests carried out in vivo or at postmortem examination in challenging cases in which FIP was confirmed or excluded based on IHC or on adequate follow-up.

Twelve cases (four without FIP, eight with FIP) were retrospectively studied. Clinical findings, serum protein electrophoresis (SPE), analysis of the effusions (AE), antifeline coronavirus serology, serum concentration of α1-acid glycoprotein (AGP) and histopathology were classified as consistent, doubtful or non-consistent with FIP. Sensitivity, specificity and concordance (κ) with the final diagnosis were calculated.

Concordance was absent for serology (κ=-0·08) and AE (κ=-0·52), poor for histopathology (κ=0·09), fair for SPE (κ=0·25) and perfect for AGP (κ=1·00). Sensitivity was high for AGP (100%) and low for AE (50%), SPE (37·5%) and histopathology (37·5%). Specificity was high for AGP or histopathology (100%) and low for SPE (50%) and AE (0%).

IHC must always be performed to confirm FIP. If this is not possible, when histopathology is controversial, elevated AGP concentrations may support the diagnosis of FIP.