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

Abstract

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.