Summary
A urine cortisol:creatinine (c:c) ratio, determined from a free-catch morning sample, was evaluated in each of 83 dogs as a screening test for hyperadrenocorticism. The dogs evaluated were allotted to 3 groups, including 20 healthy dogs, 40 dogs with confirmed hyperadrenocorticism (hac), and 23 dogs with polyuria and polydipsia not attributable to hac (polyuria/polydipsia group; pu/pd). Overlap in the urine c:c ratios (mean ± sem), comparing results from the healthy dogs (5.7 × 10-6 ± 0.9) with those from the hac dogs (337.7 × 10-6 ± 72.0) was not found. However, 11 (64%) of the 18 values from the pu/pd dogs (42.6 × 10-6 ± 9.4) were above the lowest ratio in the hac group and 50% of the hac group had a urine c:c ratio below the highest value in the pu/pd group. When the mean urine c:c ratio (± 2 sd) for the group of healthy dogs was used as a reference range, 100% of the hac dogs and 18 (77%) of 23 dogs in the pu/pd group had abnormal urine c:c ratios. The sensitivity of the urine c:c ratio to discriminate dogs with hac was 100%. The specificity of the urine c:c ratio was 22% and its diagnostic accuracy was 76%.
On the basis of our findings, a urine c:c ratio within the reference range provides strong evidence to rule out hac. However, abnormal urine c:c ratios are obtained from dogs with clinical diseases other than hac. Therefore, measurement of a urine c:c ratio should not be used as the sole screening test to confirm a diagnosis of hac.
