Background: Tubulointerstitial kidney disease is a common cause of illness and death in pet cats and is typically not associated with overt proteinuria.

Hypothesis: Proteinuria would be independently related to survival in cats with renal failure, with or without hypertension.

Animals: The study included 136 client‐owned cats; 28 apparently normal, 14 hypertensive but not azotemic, 66 azotemic but not hypertensive, and 28 both hypertensive and azotemic.

Methods: Cox's proportional hazards model was used to determine the influence of initial plasma creatinine concentration, proteinuria (urine protein‐to‐creatinine ratio or albumin‐to‐creatinine ratio), age, and systemic hypertension on the risk of death or euthanasia during the follow‐up period. Multivariable linear regression was used to determine the relation between severity of proteinuria and predictive variables, including age, plasma creatinine concentration, systolic blood pressure, sex, and urine specific gravity.

Results: Plasma creatinine concentration and proteinuria were very highly related to survival. The hazard ratio (95% confidence intervals) for death or euthanasia was 2.9 (1.4–6.3) and 4.0 (2.0–8.0) for urine protein‐to‐creatinine ratio 0.2‐0.4 and >0.4, respectively, compared with the baseline group with a urine protein‐to‐creatinine ratio of <0.2 and were 2.4 (1.2–4.8) and 4.9 (2.3–10.2) for an albumin‐to‐creatinine ratio of 30–82 mg/g and <82 mg/g, respectively, compared with a baseline group with albumin‐to‐creatinine ratio of <30 mg/g. Treated hypertensive cats did not have reduced survival, although systolic blood pressure, together with plasma creatinine concentration was positively related to the magnitude of proteinuria.

Conclusions and Clinical Importance: Despite the relatively low concentrations of proteinuria typical of chronic renal disease in cats, this measurement is of prognostic significance.