CBC-Derived Inflammatory Indices and Renal Doppler Findings in Cats with Feline Idiopathic Cystitis: A Retrospective Case-Control Study

Feline idiopathic cystitis (FIC) is a multifactorial lower urinary tract disorder in which systemic inflammatory and stress-related mechanisms may contribute to disease pathophysiology. This retrospective case control study aimed to evaluate complete blood count (CBC)-derived inflammatory indices, selected renal biochemical markers and renal Doppler ultrasonographic parameters in cats with FIC. The study included 55 cats diagnosed with FIC and 20 clinically healthy control cats. Medical records were reviewed for demographic characteristics, hematological and biochemical parameters, urinalysis, urine culture, and ultrasonographic findings. Neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), systemic immune-inflammation index (SII), systemic inflammatory response index (SIRI), and aggregate index of systemic inflammation (AISI) were calculated from absolute blood cell counts. Bilateral renal resistive index (RI) and pulsatility index (PI) were measured using Doppler ultrasonography. Cats with FIC had significantly lower lymphocyte and platelet counts and significantly higher NLR, SII, and serum urea concentrations compared with healthy controls. Creatinine and phosphorus concentrations did not differ significantly between groups. Among renal Doppler parameters, only the right renal RI differed significantly, whereas left RI and bilateral PI values showed no significant differences. Receiver operating characteristic analysis showed statistically significant but modest diagnostic performance for NLR, lymphocyte count, and SII, with NLR demonstrating the highest discriminatory ability. In conclusion, CBC-derived inflammatory indices, particularly NLR and SII, may provide useful supportive information regarding systemic inflammatory and stress-related alterations in cats with FIC. However, these markers should be interpreted as adjunctive parameters within an exclusion-based diagnostic approach.