¹Afyon Kocatepe University, Faculty of Veterinary Medicine, Department of Internal Medicine, TR-03200 Afyonkarahisar - TÜRKİYE DOI : 10.9775/kvfd.2026.36026 Chronic kidney disease (CKD) is one of the commonly observed progressive diseases in cats. Red blood cell distribution width (RDW) is a parameter that reflects variability in erythrocyte size. Recently, RDW has been shown to have potential value as a biomarker for disease severity and progression in various conditions in both human and veterinary medicine; however, information regarding its clinical significance in feline CKD remains limited. The aim of this study was to compare RDW values among cats with CKD, acute-on-chronic kidney disease, and healthy cats and to evaluate the relationship between RDW and hematological and biochemical parameters. In this study, cats with CKD, AOC, and healthy cats presented to our clinic between 2022 and 2025 were retrospectively evaluated. Cats with any concurrent endocrine, neoplastic, or infectious diseases were excluded from the study. Cats with CKD were divided into three groups: early-stage kidney disease (IRIS stages 1 and 2), advanced-stage kidney disease (IRIS stages 3 and 4), and acute on chronic kidney disease (AOC). Hematological, biochemical, and ultrasonographic findings were evaluated. One-way analysis of variance (ANOVA) and Pearson correlation analysis were performed. No significant relationships were detected between RDW and SDMA, UPC, BUN, or phosphorus (PHOS) among the study groups. Only a borderline negative correlation was identified between RDW and serum creatinine concentration (r=−0.216; P=0.050). In conclusion, although RDW may be used in other diseases or in human medicine, it does not appear to be a reliable marker for determining disease progression in feline CKD. Keywords : Cat, Chronic kidney disease, Acute-on-chronic kidney disease, RDW