Chronic Kidney Disease and Proteinuria in the Cat and Dog
Chronic renal failure is a common cause of illness and death in older cats. Histopathology often reveals diffuse tubulointerstitial nephritis as a frequent finding. Some cats with careful management will eventually die of some other cause, but regular monitoring is required to manage these cases successfully and to alter treatment accordingly. Recognised treatments include feeding diets restricted in protein and phosphate content.
A recent paper in J Vet Intern Med by Syme et al (2006) found that both plasma creatinine and proteinuria levels were very highly related to survival times. Proteinuria is an easy parameter to quantify and gives helpful information. Shortest survival times in cats with naturally occurring kidney disease were found in animals with a Urine Protein Creatinine Ratio (UPCR) of >0.4, compared to a normal value of >0.2, with intermediate values having an intermediate survival time.
It is therefore considered important when assessing a cat for renal disease to include a UPCR as part of the preliminary work up and as part of routine monitoring programmes. Systemic blood pressure also contributes to the degree of proteinuria and blood pressure measurements should also be included along with full urinalysis.
The exact effect of the proteinuria on the kidney is not yet known – is this an indicator that progressive renal injury is occurring, or is it in fact causing the progressive injury?
A study in dogs by Jacob et al in JAVMA also found a relationship in progressive worsening azotaemia and decreased survival times with the degree of proteinuria. In dogs the proteinuria is generally due to increased glomerular permeability to protein, which tends to cause a more pronounced proteinuria (>1), and is considered to be nephrotoxic in action causing, if untreated, progressive renal damage.
In all cases the existence of concurrent urinary tract inflammation or haemorrhage must be taken into account when interpreting the UPCR result. Full urinalysis with sediment examination is required. A serum assessment of protein values, with if necessary serum protein electrophoresis, must also rule out any dysproteinaemias as the cause of the proteinuria.
| UPCR LEVELS | INTERPRETATION |
| >0.2 (Dogs & Cats) | Non-proteinuric |
| 0.2 - 0.4 (Cats) 0.2 - 0.5 (Dogs) |
Borderline proteinuric |
| >0.4 (Cats) >0.5 (Dogs) |
Proteinuric |
The UPCR can be used to monitor the response to renal and blood pressure treatment, usually at 2 monthly intervals.
Further information and algorithms for the staging of Chronic Renal Disease in dogs and cats can be found on the IRIS website - www.iris-kidney.com