Cats with chronic renal failure (CRF) are often presented to veterinarians, with clinical signs ranging from subclinical to severe azotemia. A previous study of cats with CRF identified 52.6% of animals with metabolic acidosis. Chronic metabolic acidosis may lead to further renal damage. Assessment of acid-base status of patients seen in practice is challenging, as samples must be analyzed at the patient side, and the necessary equipment is expensive. The goal of this study was to determine whether biochemical evidence of metabolic acidosis could be detected before deterioration of excretory renal function.

Cases of CRF were seen 2 to 4 weeks after initial diagnosis and then every 6 weeks thereafter. Management was tailored to each cat's condition. Standard care included transitioning to a phosphate- and protein-restricted diet (depending on owner compliance), treatment of urinary tract infections, and antihypertensive therapy for cats with systolic pressure over 175 mm Hg and/or ocular or CNS signs of hypertension. Some cats received oral potassium gluconate therapy. Fifty-five cats with CRF entered the study. Thirty-four of the cats showed no evidence of deterioration of renal function over time (group 1), 14 cats showed acute deterioration in renal function (group 2), and 7 showed gradual progressive increases in creatinine levels (group 3). Only one cat in group 1 developed metabolic acidosis, losing more than 10% of its body weight over the next 3 months, and was euthanized. Cats in groups 2 and 3 were further categorized based on progression of disease. Most owners did not recognize when their cats' condition deteriorated. Weight loss was the most reliable objective indicator of deterioration. Biochemical evidence of acid-base disturbances occurred when the cats progressed to the "severe" category based on creatinine levels. More studies need to be done to determine if nonacidotic feline CFR cases would benefit from bicarbonate precursors.

COMMENTARY: This report suggests that metabolic acidosis may be much less common in cats with chronic renal failure than previously reported: it primarily occurs in cats with very advanced disease, and it may not be a cause of progression of early chronic renal failure. Regardless, cats with chronic renal failure should be tested for this disorder and treated as required.

Acid-base balance of cats with chronic renal failure: effect of deterioration in renal function. Elliott J, Syme HM, Markwell PJ. J SMALL ANIM PRACT 44:261-268, 2003.