Update on clinicopathological assessment of renal health in non-racing greyhounds

Abstract

Background: Serum creatinine concentrations differ in greyhounds compared with non-sighthounds, but it is not known whether urine creatinine concentrations also differ and whether any difference would influence the interpretation of the urine protein to creatinine ratio (UPC). Additionally, there is some evidence for greyhounds having higher serum symmetric dimethylarginine (SDMA) than non-sighthounds, but this has yet to be confirmed in healthy non-racing greyhounds. Objectives: The objectives of this study were fourfold: (1) to compare the urine creatinine concentrations in healthy greyhounds and a control group of healthy non-sighthounds, (2) to determine the UPC reference interval in healthy greyhounds and to compare this with the UPC reference interval in a control group of healthy non-sighthounds, (3) to determine the serum SDMA concentration reference interval in healthy greyhounds and to compare this with the serum SDMA concentration reference interval in a control group of healthy non-sighthounds and with a previously established canine serum SDMA concentration reference interval, and (4) to establish whether lean body mass is correlated with serum creatinine and urine creatinine concentrations in greyhounds. Methods: The study used an observational cross-sectional design and included 98 clinically healthy non-racing greyhounds and 24 non-sighthound dogs with similar weight, age and sex distributions, as determined by t-test and chi-squared tests. SDMA, urine creatinine concentration and UPC values were measured from blood and urine samples. Linear regression was used to compare the greyhound and non-sighthound groups. Greyhound reference intervals were determined for SDMA and UPC using non-parametric methods. These were compared with the reference intervals for the non-sighthound group and with current International Renal Interest Society guidelines. In the greyhound sample, the association of urine creatinine with thigh circumference, height and weight was estimated using Pearson correlation. Statistical significance was set at P < 0.05 for all analyses. Results: Mean urine creatinine was approximately 22% higher in greyhounds than non-sighthounds after adjusting for urine concentration (P < 0.05). The upper limit of the greyhound UPC reference interval was 0.20 or 0.42, depending on whether strict or moderate exclusion criteria, respectively, were applied. The mean UPC was 29% lower in greyhounds than non-sighthounds, but this difference was not statistically significant (P = 0.1). The serum SDMA reference interval for greyhounds was 6.3–19.7 µg/dL (0.31–0.98 µmol/L). The upper end of this interval was higher than the upper limit of the published canine reference interval (6–13 µg/dL), and the mean concentration was statistically significantly higher in greyhounds (13.0 µg/dL) than non-sighthounds (10.2 µg/dL, P < 0.001). In greyhounds, there were weak correlations between the three morphometric measurements and both serum creatinine and urine creatinine after adjusting for urine concentration. Conclusions and clinical importance: These findings provide further evidence that greyhounds require several breed-specific reference intervals when evaluating renal function. Apart from having higher serum creatinine, greyhounds also have higher SDMA and higher urine creatinine when compared to non-sighthounds. Although UPC trended slightly lower in greyhounds, this finding was not significant, and therefore the threshold for non-proteinuria set by IRIS guidelines appears to be appropriate for greyhounds based on the calculated reference interval.