INTRODUCTION Chronic kidney disease

INTRODUCTION Chronic kidney disease (CKD) is the most common disease affecting the kidneys of dogs and cats.It may be recognized by reduced kidney function or the presence of kidney damage. CKD is defined as kidney damage present for at least three months, with or without decreased glomerular filtration rate (GFR) or greater than 50% reduction in GFR persisting for at least three months (Polzin et al, 2005). Kidney damage is further defined as either 1) microscopic or macroscopic pathologic changes detected by histologic or direct visualization of the kidneys or 2) markers of damage detected by blood or urine tests or imaging studies.In the past, multiple terms were used to define the severity of renal functional abnormalities including renal insufficiency,renal failure and uremia.However,there has not been uniform agreement on the specific definition of renal insufficiency vs. renal failure. Therefore, it has been recently proposed by the International Renal Interest Society (IRIS) to replace these terms with a scheme to classify severity of CKD into four stages based on stable serum creatinine concentrations (Table 37-1).Two of the foundational assumptions inherent in this classification scheme are that the presence of CKD has been confirmed and that azotemia, if present, has been localized as renal in origin. This classification schemeemphasizes the continuum of severity of renal injury of dogs and cats with documented presence of kidney damage without evidence of azotemia in stage 1 CKD, to progressively more severe CKD with resultant increasing serum creatinine concentration for stages 2 to 4.Furthermore,by using the term “kidney disease”and staging the severity of disease,it is possible to facilitate understanding, communication and application of management guidelines for patients in each stage. The goals of this chapter are to provide pathophysiologic concepts and practical nutritional management recommendations for dogs and cats with CKD.Nutritional management of patients with CKD includes measures to reduce signs of uremia and slow progression to later stages of disease.There is general agreement regarding nutritional management of CKD when overt signs exist; however, the role of nutritional intervention during earlier stages of CKD is less well defined. Thus, in a sense, the question is not whether to use nutritional management but when should it be initiated. Because detection of CKD in its early stages is difficult and there appears to be no harm in avoiding nutrient excess (e.g.,phosphorus) during earlier stages, nutritional management should be considered by stage 2 CKD and is clearly indicated when serum creatinine exceeds 2 mg/dl (179 µmol/l) (Jacob et al, 2002; Ross et al, 2006). Similarly, significant and persistent renal proteinuria,