In dogs and humans, the measurement of urinary
corticoid excretion has become a standard screening test for the diagnosis of
hyperadrenocorticism. Mainly because the urinary excretion of
cortisol was considered to be very low in cats, its measurement was not used in the diagnosis of
hyperadrenocorticism in this species. We therefore studied the urinary excretion of [3H]
cortisol and measured the
corticoid/
creatinine (C/C) ratio in healthy cats and in cats with
hyperadrenocorticism in order to evaluate the applicability of this measurement in the diagnosis of feline
hyperadrenocorticism. The median urinary excretion of intravenously administered [3H]
cortisol was 1.85% (measured as excreted 3H; range, 1.56 to 1.99; n = 4). High-performance liquid chromatography analysis showed a small peak of
cortisol and a large peak consisting primarily of conjugates of
cortisol and/or its metabolites. The 2.5 and 97.5 percentiles of the urinary C/C ratio in healthy cats were 2 x 10(-6) to 36 x 10(-6) (n = 42). The C/C ratio was significantly higher in six cats with pituitary-dependent
hyperadrenocorticism (median, 122 x 10(-6); range 51 x 10(-6) to 272 x 10(-6)). The administration of a high dose of
dexamethasone (0.1 mg/kg thrice daily per os) led to marked suppression of the C/C ratio in healthy cats (median suppression of the average of the C/C ratio of the first two consecutive days was 92%; range, 74 to 96%; n = 12), as well as in five cats with pituitary-dependent
hyperadrenocorticism.(ABSTRACT TRUNCATED AT 250 WORDS)