As you know, chronic renal disease is a common condition in geriatric cats. However, by the time it is diagnosed based on
elevated plasma creatinine concentrations, a large percentage of functioning kidney mass may have been lost. Researchers in
the United Kingdom aimed to identify clinical predictors of azotemia development in older healthy cats. The participating
cats were followed for a minimum of one year, and the urine protein-to-creatinine ratio, urine albumin-to-creatinine ratio,
and NAG, a urinary enzyme, were evaluated as potential predictors for the development of azotemia.
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Cats selected for the study were over 9 years of age and thought to be healthy by their owners. Each animal was thoroughly
assessed, including a complete history, physical examination, and evaluation of blood and urine samples. Systolic blood pressure
measurements and a fundic examination were also used to evaluate each cat. Individuals with systemic hypertension were treated
and managed throughout the study. Azotemic and hyperthyroid cats were excluded. The cats were reevaluated at six-month intervals,
and, after stabilization, hypertensive cats were evaluated every two months.
Azotemia was diagnosed during the one-year period in more than 30% of the cats participating. No correlation was seen between
hypertension and the development of azotemia. However, for those cats that developed azotemia during the study, there were
significant increases in plasma creatinine, urea, and phosphate concentrations and decreases in urine specific gravity, body
weight, and packed cell volume.
Only proteinuria was consistently associated with the development of azotemia. Interestingly, the urine protein-to-creatinine
ratio proved more predictive of azotemia development than the urine albumin-to-creatinine ratio. Those cats that developed
azotemia did have a lower urine specific gravity and higher plasma urea and creatinine concentrations at initial evaluation
than did those that remained nonazotemic. These initial values were all within the laboratory reference ranges but were significantly
different in the two groups. Urine specific gravity also decreased significantly in the cats from the beginning of the study
to the development of azotemia. NAG index, one of the variables evaluated, correlated with the urine protein-to-creatinine
ratio and was significantly higher in cats that became azotemic. However, it did not prove to be of any additional benefit
as a predictor of azotemia.
The researchers concluded that the urine protein-to creatinine ratio is a relatively inexpensive test that requires only a
small volume of urine. Monitoring this parameter in conjunction with the plasma creatinine concentration should be part of
geriatric screening programs in cats. As cats age, their risk of developing chronic renal failure increases dramatically,
and identifying early renal disease may greatly improve the outcome for these patients.
Source: Jepson RE, Brodbelt D, Vallance C, et al. Evaluation of predictors of the development of azotemia in cats. J Vet Intern Med 2009;23(4):806-813.