Kooistra HS, de Lange M, Trip MRJ, Rijnberk A: Urinary corticoid/creatinine ratios in cats with hyperthyroidism. Proceedings of the 12th annual congress of the European College of Veterinary Internal Medicine-Companion animals, 2002.

Elevated urinary corticoid/creatinine (C/C) ratios in cats with signs and symptoms compatible with hyperadrenocorticism have been reported to be indicative of hyperadrenocorticism. However, in addition to stress, diseases other than hyperadrenocorticism may also result in elevated urinary C/C ratios. Because many of the signs and symptoms of feline hyperadrenocorticism may also be found in cats with hyperthyroidism, the purpose of this study was to determine whether cats with hyperthyroidism may also have elevated urinary C/C ratios.

From 32 cats with hyperthyroidism (ages ranging from 9 to 18 years) and 43 healthy cats (ages ranging from 7 to 18 years) urine samples were collected at home on two consecutive days. From 6 cats the owners also collected 2 urine samples 3 months after successful treatment of hyperthyroidism. The measurements of the two urine samples were averaged and expressed as basal urinary C/C ratio.

The urinary C/C ratios in the cats with hyperthyroidism (median 37.5 x 10-6; range 5.9 x 10-6 to 169.5 x 10-6) were significantly higher than those in the healthy cats (median 16 x 10-6; range 5 x 10-6 to 52 x 10-6). The urinary C/C ratios in the 6 hyperthyroid cats before treatment were significantly higher than those after successful treatment.

In conclusion, the results of this study demonstrate that elevated urinary C/C ratios may be found in cats with hyperthyroidism, which could falsely be ascribed to Cushing's syndrome.