De Ritis Ratio and L-FABP as Supportive Biomarkers of Hepatic Involvement in Cats with Effusive FIP

Feline infectious peritonitis (FIP), caused by feline infectious peritonitis virus (FIPV), is a systemic disease affecting multiple organs. Although routine biochemical parameters are not diagnostic, they may aid in clinical suspicion. The aim of this study was to investigate the clinical utility of the De Ritis ratio (AST/ALT) and liver-type fatty acid-binding protein (L-FABP) as candidate biomarkers of liver-associated biochemical alterations in cats with effusive FIP. A total of 47 client-owned cats naturally infected with feline coronavirus (FCoV) were included: 37 cats with suspected effusive FIP (thoracic effusion, n = 14; abdominal effusion, n = 23) and 10 FCoV-positive asymptomatic cats as controls. FIPV infection was confirmed by RT-PCR of thoracic or abdominal effusion samples in all cats with suspected effusive FIP. Control cats were clinically healthy, FCoV-positive by fecal RT-PCR, and had no evidence of FIPV infection. The De Ritis ratio was significantly higher in cats with abdominal effusive FIP than in asymptomatic FCoV-positive controls and demonstrated excellent discriminatory performance for identifying abdominal effusive FIP (AUC = 0.843) and effusive FIP overall (AUC = 0.808). Although serum L-FABP concentrations did not differ significantly between groups, ROC analysis demonstrated acceptable-to-excellent discriminatory performance for cats with effusive FIP (AUC = 0.730-0.854), suggesting complementary rather than standalone clinical utility. These findings suggest that the De Ritis ratio may represent a supportive indicator of liver-associated biochemical alterations in cats with effusive FIP, whereas the clinical utility of L-FABP remains preliminary and warrants further clinical validation.