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Evaluation of Proteinuria in Hyperthyroid Cats

Syme H.M. and Elliott J.

Conference Proceedings, (2001). American College of Veterinary Internal Medicine, Denver:

Many cats are diagnosed with renal failure (RF) following treatment for hyperthyroidism.It is uncertain whether this is due to the deleterious effects of hyperthyroidism per se or is a reflection of the high incidence of RF in the geriatric feline population. This study was designed to determine the incidence of proteinuria in cats before and after treatment for hyperthyroidism and to correlate these findings with the development of azotemia. In addition, urinary albumin as measured as a putative marker of structural and hemodynamic glomerular injury. Urine samples were obtained from cats prior to, and following, treatment for hyperthyroidism. Treatment was with carbimazole therapy alone, or combined with thyroidectomy. Urine protein and creatinine concentrations were measured by standard clinical laboratory methods and urinary albumin was measure by an ELISA validated for use in the cat. Cats were excluded from the study if they were in RF prior to treatment, if a urinary tract infection was diagnosed, or if euthyroidism and plasma creatinine concentrations were not adequately documented during a 6 month follow up period. The plasma creatinine concentration at 6 months was used to define 2 groups, cats in RF (creatinine > 1.9 mg/dl) and cats not in RF (NRF). Pre-treatment urine protein:creatinine (UPR) and urine albumin:creatinine (UAC) in these two groups were compere by the Mann-Whitney U test. The Wilcoxon signed rank test was used to compare UPC and UAC pre and post treatment. Data are reported as median values [25th, 75th percentiles].
Of the 25 cats (12 RF, 13 NRF) included in the study, 13 (52%) had UPC >0.5, and 5 (20%) had UPC > 1.0 prior to treatment. The UPC before treatment did not differ between the RF and NRF groups (0.50 [0.27, 1.42] vs. 0.51 [0.26, 0.82]. UPC decreased significantly (p=0.001, n=19) from 0.49 [0.26,0.95] to 0.23 [0.10, 0.33] following treatment. The UAC was not different between the RF and NRF groups before treatment (48 [11, 106] x 10-3 vs. 45 [19, 67] x 10-3) and decreased significantly (P=0.03, n=19) from 42 [13, 64] x 10-3 to 20 [9, 40] x 10-3 following treatment.
In summary, many hyperthyroid cats have significant urinary loss of proteins including albumin. The magnitude of proteinuria can not be sued to predict which cats will develop RF when euthyroid. Proteinuria resolves following treatment of hyperthyroidism in most cats including many that develop azotemia.