Diagnostic utility of serum amyloid A, procalcitonin and hematology-derived inflammatory indices in cats naturally infected with feline panleukopenia virus.

Feline panleukopenia virus (FPV) infection is a highly contagious and potentially fatal disease of cats, characterized by intestinal injury, bone marrow suppression and systemic inflammatory alterations. This study evaluated the diagnostic utility of serum procalcitonin (PCT), serum amyloid A (SAA), selected biochemical variables and hematology-derived inflammatory indices in cats naturally infected with FPV. Fifty-nine cats were enrolled between February 2024 and December 2025, including 28 cats with naturally occurring FPV infection and 31 healthy controls. FPV infection was diagnosed using a fecal FPV antigen rapid test. Complete blood count variables were recorded, and serum concentrations of PCT, SAA, albumin (ALB), total protein, globulin, magnesium and glucose (GLU) were measured. Hematology-derived inflammatory indices, including neutrophil-to-lymphocyte ratio, monocyte-to-lymphocyte ratio, platelet-to-lymphocyte ratio, derived neutrophil-to-lymphocyte ratio, aggregate index of systemic inflammation (AISI), systemic inflammatory response index (SIRI) and systemic immune-inflammation (SII) index, were calculated. Cats with FPV infection had significantly higher SAA concentrations than healthy cats, with median values of 174.05 µg/mL and 5.00 µg/mL, respectively. Serum GLU was also higher in the FPV group, whereas ALB concentration was lower. White blood cell, neutrophil, lymphocyte, monocyte, eosinophil, basophil and platelet counts differed significantly between groups. Several inflammatory indices, particularly AISI and SIRI, showed strong diagnostic performance, with area under the receiver operating characteristic curve values of 0.92 and 0.91, respectively. DeLong analysis showed no significant difference between the diagnostic performance of these indices and SAA. In contrast, serum PCT did not show diagnostic utility and was not correlated with any biochemical variable. These findings indicate that SAA is an excellent diagnostic biomarker in cats naturally infected with FPV. In addition, selected hematology-derived inflammatory indices, particularly AISI and SIRI, may serve as practical and cost-effective adjunctive tools derived from routine complete blood count data. Serum PCT appears to have limited value in the diagnostic assessment of primary viral FPV infection.