URINARY CORTICOID CREATININE RATIOS IN THE DIFFERENTIATION BETWEEN PITUITARY-DEPENDENT HYPERADRENOCORTICISM AND HYPERADRENOCORTICISM DUE TOADRENOCORTICAL TUMOR IN THE DOG/

In a study on the differentiation between pituitary-dependent hyperadr enocorticism (PDH) and hyperadrenocorticism due to adrenocortical tumo ur (AT), two questions were addressed: 1. Do basal urinary corticoid/c reatinine (c/c) ratios have any value in this respect, and 2, what is the reference percentage suppression of the urinary c/c ratios in the high-dose dexamethasone suppression test? Data obtained from 160 dogs with hyperadrenocorticism were analysed, In 49 dogs the diagnosis AT w as confirmed by the finding of plasma ACTH concentrations < 40 ng/l, b y visualisation of the tumour by ultrasonography and/or computed tomog raphy, and by histological examination of the adrenal tissue obtained at surgery or autopsy, Among the 111 dogs with PDH, there were 31 anim als with resistance to dexamethasone suppression, i.e., suppression < 50%, The basal urinary c/c ratios of dogs with PDH and AT did not diff er significantly, although urinary c/c ratios > 100 x 10(-6) almost ex clusively occurred in association with PDH, Among the dogs with hypera drenocorticism, the positive predictive value of a basal urinary c/c r atio > 100 x 10(-6) for the diagnosis of PDH was 0.90 ( 95% CI: 0.74 - 0.98). Of the 49 dogs with AT, 34 had a urinary c/c ratio after dexam ethasone administration higher than the basal urinary c/c ratio, The m aximum suppression of the basal urinary c/c ratio in dogs with AT was 43.7%, It is concluded that in dogs with hyperadrenocorticism basal ur inary c/c ratios only have predictive value in the differentiation bet ween AT and PDH when the ratio exceeds 100 x 10(-6), The generally acc epted criterion of 50% suppression by dexamethasone in the differentia tion between PDH and AT is also applicable to the urinary de ratio.