Determination of and correlation between urine protein excretion and urine protein-to-creatinine ratio values during a 24-hour period in healthy horses and ponies

Abstract

OBJECTIVE-To determine whether urine protein-to-creatinine (UP:C) ratio assessment provides an estimate of urine protein excretion (UPE) over a 24-hour period in horses and ponies, establish a preliminary UP:C ratio reference range, and determine UP:C ratio variation over time in healthy equids. ANIMALS-11 female horses and 6 female ponies. PROCEDURES-Urine was collected from all equids at 4-hour intervals for 24 hours. Total 24-hour UPE (mg of protein/kg of body weight) and UP:C ratio were determined; these variables were also assessed in aliquots of urine collected at 4-hour intervals. On 2 additional days, urine samples were also obtained from 6 horses (1 sample/horse/d) to determine day-to-day variation in UP:C ratio. Correlation between 4-hour or 24-hour UPE and UP:C ratio values was assessed. Reference ranges for 24-hour UPE, 24-hour UP:C ratio, and 4-hour UP:C ratios were calculated as central 95th percentiles of observed values. RESULTS-Mean 24-hour UPE (4.28 +/- 2.99 mg/kg) and 24-hour UP:C ratio (0.0 to 0.37) had excellent correlation (R = 0.826; P < 0.001) in both horses and ponies; analysis of 4-hour data also revealed good correlation (R = 0.782; P < 0.001) with these variables. Calculated UPE and UP:C ratio reference ranges were similar to established ranges in other species. Day-to-day variability in UP:C ratio was minimal, and all results were within the reference range calculated by use of the 24-hour urine samples. CONCLUSIONS AND CLINICAL RELEVANCE-Assessment of the UP:C ratio appears to be a reliable method for estimating 24-hour UPE in horses and ponies.