Immunoreactive cortisol measurement in canine urine and its validity in hyperadrenocorticism diagnosis

The aim of this study was to compare two methods of immunoreactive cortisol determination in urine and an assessment of the validity of urine cortisol /creatinine ratio (UCCR) in dogs. The UCCR was measured in three groups of dogs: (1) healthy dogs, (2) dogs with hyperadrenocorticism and (3) dogs suf fering from other diseases presented with polyuria and polydipsia (PU/PD). All cortisol measurements in urine were performed using two methods: (1) fl uorescence polarisation immunoassay (FPIA) with urine extraction and (2) ra dioimmunoassay (RIA) without urine extraction. Paired results of 30 cortiso l measurements and 30 UCCR were compared using the Wilcoxon test. It was pr oved that the differences between the two methods (i.e., FPIA with urine ex traction and RIA without urine extraction) were highly statistically signif icant (p < 0.01). While in the cortisol measurement using the FPIA with uri ne extraction the median of the UCCR amounted to 18.53 x 10(-6), in the RIA without urine extraction it was 37.83 x 10(-6). Values of the UCCR in indi vidual canine groups were also compared with each other. The UCCR in dogs w ith hyperadrenocorticism was higher (p < 0.01) than in healthy dogs or dogs presented with the PU/PD signs. There were also found significant differen ces (p < 0.05) between the UCCR in healthy dogs and dogs presented with PU/ PD signs. Both methods of immunoreactive cortisol determination in urine ca n be used for clinical diagnosis of hyperadrenocorticism, however, the abov e mentioned differences should be considered.