Chronic Renal Disease

Renal disease in older animals usually develops over a long period of time with clinical signs appearing late in the course of the disease. Polydipsia and polyuria signal a loss of urine concentrating ability and typically develop prior to azotemia. The urine does not suddenly become isosthenuric, but the maximum specific gravity gradually declines to this level, provided the animal survives to this stage. The term renal insufficiency is often applied to the stage of compensation where azotemia is mild, the animal is experiencing polyuria and polydipsia but is, otherwise, feeling well, and the USG is within the range between isosthenuria and concentrated. The term renal failure may be reserved for a more advanced disease where isosthenuria is present along with significant azotemia and clinical illness. Renal disease is a more general term which encompasses all forms of renal pathology. However, there is not universal acceptance of these definitions in veterinary medicine.

Animals may experience weight loss, lethargy, weakness, and occasional vomiting, all due to biochemical changes related to renal disease. Typical laboratory findings are hyperkalemia, high anion gap metabolic acidosis (due to renal acid retention), hyperphosphatemia, and renal azotemia. Nonregenerative anemia is a common sequela to chronic renal disease in all animals. The lack of erythropoietin leads to a gradual decrease in hematocrit. The rate of development of azotemia does not always correlate well with the rate of development of anemia, so that many animals develop serious illness and clinical signs of renal failure before developing anemia.

End-stage renal failure is associated with the clinical condition known as uremia which includes dehydration, vomiting, diarrhea, inappetence, lethargy, “uremic” ulcers in the oral cavity and GIT, breath odour, and central nervous signs. Although polyuria is seen in the compensatory stage of the disease, oliguria or anuria may occur terminally.