Plasma creatinine (P-creatinine) is considered as the best indirect indicator of renal function and used for staging of chronic kidney disease. Nevertheless, to our knowledge, no rational definition of reference interval for P-creatinine has been published in the feline species. The objective of the present study was to determine the reference interval of P-creatinine in 4 major feline breeds.

Blood was collected on heparinised tubes in fasted clinically healthy owned cats. Blood was immediately centrifuged. Plasma was harvested and stored at -20°C until assay by the enzymatic method using an analyzer (Vitros 250 chemistry system, Ortho-Clinical Diagnostics, Raritan, NJ). Data (without or with logarithmic transformation) were tested for normality by Kolmogorov-Smirnov test. Effect of breed, body weight (BW), age and gender was assessed using a general linear model.

Birman (n=137), Chartreux (n=134), Maine Coon (n=143), and Persian (n=141) cats were sampled. The corresponding reference intervals (RI) were 1.0-2.8 mg/dL, 0.7-2.3 mg/dL, 0.7-2.2 mg/dL, and 0.8-1.9 mg/dL, respectively. A higher P-creatinine (P<0.001) was observed in Birman breed compared to the others. P-creatinine increased (P<0.05) with age in all breeds, and with BW in Birman, Chartreux and Maine Coon. P-creatinine was higher (P<0.05) in female than male Birman cats.

In conclusion, breed, age, and BW should be considered when interpreting basal P-creatinine in cats.