Feline chronic kidney disease (CKD) is one of the most common metabolic disorders in cats worldwide. The diagnosis of early or nonazotemic CKD is challenging and screening is strongly recommended. However, studies on cats with nonazotemic CKD are scarce, simple and straightforward criteria to define nonazotemic CKD are lacking and reliable diagnostic tools to detect this population are urgently needed. Nonazotemic CKD is expected to be characterized by diffuse or regional renal hypoxia or hypoperfusion, presence of renal fibrosis and decreased GFR. The overall aim of this project is to better characterize nonazotemic CKD cats by the following specific objectives (1) to validate and assess clinical applicability of Volumetric Absorptive Microsampling (VAMS) to perform more feline-friendly GFR measurements; (2) to objectify renal function of nonazotemic CKD cats by estimating GFR (3) to evaluate Shear Wave Elastography (SWE) as early indicator of the degree of renal fibrosis in cats with nonazotemic CKD and (4) to assess the applicability of functional MRI techniques Arterial Spin labeling (ASL) and Blood Oxygenation level-dependent (BOLD) to detect local or generalized renal perfusion and -oxygenation changes. The results of this proposal will lead to a better understanding of the pathogenesis of spontaneous feline CKD, improved definition of nonazotemic CKD in cats, optimize screening protocols for CKD and give scientific research for novel early biomarkers the needed boost.