Staging of chronic kidney disease
There are four stages of chronic kidney disease (CKD) in The International Renal Interest Society (IRIS) staging system. The
four stages are based on serum creatinine, with two substages based on hypertension and proteinuria. The risk associated with
hypertension is stratified and further categorized if hypertensive complications are present. A urine protein:creatinine ratio
(UPC) < 0.2 is non-proteinuric, 0.2-0.4 is borderline, and > 0.4 is proteinuric.
In one study of 45 cats with Stage II or III CKD, none of the cats fed a renal diet (Hill's K/D) died of renal causes or had
a uremic crisis during the 2 year study, compared to 22% renal-related deaths and 26% suffering a uremic crisis in the cats
fed a maintenance diet. In a canine CKD study, dogs eating a renal diet lived twice as long as dogs eating a maintenance diet.
A renal diet should have a restricted quantity of high biologic value protein, and should be restricted in phosphorus. Excessive
salt restriction may promote activation of the renin-angiotensin-aldosterone system and inappropriate kaliuriesis leading
to hypokalemia, without beneficial effect on blood pressure. Decreasing the ratio of omega-6 to omega-3 essential fatty acids
may have some renoprotective effect; this area deserves further study. Phosphate restriction in the diet will help reduce
renal secondary hyperparathyroidism and renal mineralization, and can thus help slow progression and provide a better quality
Over 40% of cats with CKD have a diminished appetite. Several drugs have been used to stimulate appetite, including diazepam,
oxazepam, and cyproheptadine. A new drug, mirtazapine (Remeron), has been used anecdotally to increase appetite and control
nausea. A dose reduction is recommended because it is partially excreted by the kidney, and serotonin syndrome may occur as
a side effect. No studies on its use in cats with CKD have been published.
Any diet change should usually be delayed until the pet is eating well at home. Changing to a renal diet may take 3-4 weeks,
and weekly phone calls help to encourage clients to remain compliant.
Multiple methods are available to assess proteinuria. The urine dipstick is unreliable for detecting proteinuria, with a sensitivity
of 37% and specificity of 75%. Many urine samples with a positive dipstick reading (trace or higher) may have a urine protein:creatinine
ratio (UPC) less than 0.5. A microalbuminuria test (Heska Corp) was positive in 110 out of 324 feline urine samples; 16 of
the 324 had a UPC over 0.4. There does not appear to be an advantage to urine albumin:creatinine ratio compared to urine protein:creatinine
ratio. In dogs, one UPC measurement is adequate to reliably estimate UPC when < 4. When monitoring changes in UPC over time,
a change of 80% is needed to demonstrate a significant difference when the UPC is around 0.5.