URINARY-EXCRETION OF GLUCOCORTICOIDS IN THE DIAGNOSIS OF HYPERADRENOCORTICISM IN CATS

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 [H-3]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 [H-3]cortisol was 1.85% (measured as excreted H-3; 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 CIC 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. Our results demonstrate that despite the low urinary excretion of injected [H-3]cortisol, urinary corticoid concentrations in cats can be measured by radioimmunoassay and that the urinary C/C ratio is a sensitive test in the diagnosis of hyperadrenocorticism in the cat.