Stability of glomerular and tubular renal injury biomarkers in canine urine after 4 years of storage.

Urine biomarkers are sensitive indicators of early-stage renal injury, consequently, research in this area is expanding in both human and veterinary medicine. However, studies investigating the impact of preanalytical factors, such as storage conditions, on urine biomarker concentrations are largely lacking in veterinary medicine. Therefore, we evaluated the stability of several renal injury biomarkers in canine urine after storage for 4 y at -72°C. Urine samples were collected from 26 dogs: 18 dogs with babesiosis and 8 healthy dogs. Concentrations of urine immunoglobulin G (uIgG), urine C-reactive protein (uCRP), and urine retinol-binding protein (uRBP) were measured, using validated commercial immunoassays, at the start of the study and 4 y later. To investigate the effect of long-term storage, absolute and relative differences between both measurements were compared. Additionally, dogs with babesiosis were compared with the healthy controls at both time points. Storage caused significant absolute and relative decreases in concentrations of all 3 biomarkers. Significant differences between dogs with babesiosis and healthy dogs were found in uIgG and uRBP at both times; however, the difference in uCRP between both groups lost significance after storage. Because the main goal of these urine biomarkers is to detect early-stage renal injury, the statistically significant decrease in their concentrations will be clinically relevant when a mild degree of renal injury is present. Our data indicate that the investigated urine biomarkers show significant decay after 4 y of storage at -72°C, adversely affecting their diagnostic utility.