Feline pancreatitis (FP) represents a significant clinical challenge in cats. Current gold-standard diagnosis relies on the combination of serum feline pancreatic lipase immunoreactivity (fPLI) measurement and abdominal ultrasonography (AUS). Although these methods provide high specificity, they are costly and require considerable time. A rapid, inexpensive screening tool with high sensitivity capable of reliably excluding FP during the initial consultation would therefore be highly valuable. To assess the diagnostic performance of routine complete blood count (CBC)-derived inflammatory parameters for detecting FP, 73 client-owned cats presenting with lethargy and reduced appetite for ≥2 days were prospectively enrolled. Cats were categorized as very low risk for FP if fPLI ≤3.5 μg/L and AUS negative, or as increased risk for FP with any other result combination. Seven CBC parameters were then evaluated for association with FP risk using multivariable logistic regression. Five CBC parameters showed significant association with increased FP risk: total leukocyte count (WBC; crude OR = 12.2; 95% CI: 1.52–98.5), total neutrophil count (crude OR = 5.84; 95% CI: 1.22–27.9), band neutrophil count (BNC; crude OR = 6.67; 95% CI: 1.98–22.4), neutrophil-to-lymphocyte ratio (crude OR = 3.68; 95% CI: 1.25–10.9), and eosinophil count (EC; crude OR = 0.34; 95% CI: 0.12–0.96). A diagnostic model incorporating WBC, BNC, and EC demonstrated at least fair accuracy (AUC = 82.7%; 95% CI: 72.8–92.5%). Defining a negative test as WBC < 18 G/L, BNC < 0.27 G/L, and EC > 0.3 G/L (any other combination = positive) yielded high sensitivity (91.8%; 95% CI: 80.8–96.8%) with moderate specificity (58.3%; 95% CI: 38.8–75.5%). A simple combination of three routine CBC parameters offers an immediately available, cost-effective screening tool to identify cats with lethargy and anorexia that are at elevated risk of FP.
