# Urinary Corticoid-to-Creatinine Ratio 8 Hours After Low-Dose Oral Dexamethasone for the Diagnosis of Cushing’s Syndrome in Dogs

## TL;DR

A new non-invasive test for diagnosing Cushing’s syndrome in dogs uses a low-dose oral dexamethasone and urine samples collected at home.

## Contribution

The study introduces a minimally invasive oral dexamethasone suppression test using urinary corticoid-to-creatinine ratios as a valid diagnostic alternative for Cushing’s syndrome in dogs.

## Key findings

- The oral test achieved 95% sensitivity and 93% specificity for diagnosing Cushing’s syndrome.
- 86% of dog owners preferred the oral method over the intravenous version due to reduced stress.
- Urinary corticoid-to-creatinine ratio 8 hours after administration provided the highest diagnostic accuracy.

## Abstract

The lack of suppression of serum cortisol 8 h after a low dose of intravenous dexamethasone is the most accurate test for diagnosing Cushing’s syndrome in dogs, but its performance may cause stress for both the dog and owner because it requires several venipunctures. To reduce this problem, the test was evaluated in a home setting by administering a low dose of dexamethasone orally and measuring the urinary corticoid-to-creatinine ratio before and 8 h after administration. In 168 dogs (86 with Cushing’s syndrome), the 8 h sample showed high diagnostic accuracy for Cushing’s syndrome, with a sensitivity of 95% and specificity of 93%. In addition, its preference by 86% of owners over the intravenous version supports the oral method as a valid and clinically useful diagnostic option.

The intravenous low-dose dexamethasone suppression test (IV-LDDST) is considered the most accurate method for diagnosing Cushing’s syndrome (CS) in dogs, but its intravenous administration and repeated hospital sampling are stressful and time-consuming for both dogs and owners. This study evaluated an oral LDDST (O-LDDST) as a minimally invasive alternative. The approach is based on the urinary corticoid-to-creatinine ratio (uCC) measured in urine samples collected at home at baseline (B-uCC) and 8 h after administering a low oral dose of dexamethasone (0.01 mg/kg; 8h-uCC). A total of 168 client-owned dogs were prospectively recruited: 42 healthy dogs (HD), 40 dogs with disease mimicking CS (DMCS), and 86 dogs with confirmed CS. An ROC curve analysis showed that dogs with CS had significantly higher B-uCC and 8h-uCC and a lower suppression percentage (%S) compared with HD and DMCS (all p < 0.0001). Optimal cut-offs were B-uCC > 14.2 × 10−6, 8h-uCC > 6.7 × 10−6, and %S < 48.6%, yielding sensitivity/specificity of 82.9%/83.3%, 95.3%/92.6%, and 86.0%/85.3%, respectively. O-LDDST was preferred by 85.9% of owners, although it did not distinguish pituitary- from adrenal-dependent CS. The O-LDDST proved to be a reliable, accurate, and minimally invasive diagnostic option for CS in dogs, with 8h-uCC providing the highest accuracy.