Determination of 24-Hour Urine Protein Excretion and Correlation with Random-Sample Urine Protein:Creatinine Ratio in Equids
ACVIM 2008
B. Uberti; D.B. Eberle; G.E. Moore; B.M. Pressler; J.E. Sojka
Purdue University
West Lafayette, IN, USA

Normal urine protein excretion has been determined in a variety of species, including people, dogs, and cats. Excess urine protein loss of renal origin may occur due to primary renal diseases affecting the glomeruli, or secondary to systemic inflammatory diseases, presumptively secondary to inflammation. Proteinuria may be a useful early marker of inflammatory disease. The purpose of this study was to determine 24-hr urine protein excretion in normal equids and determine how well this value correlates with random-sample urine protein:creatinine ratio (UPC).

Urine was collected from 6 random-source adult mares and 6 adult female ponies. All animals were normal based on physical examination at the time of enrollment in the study, barren, and remained healthy throughout the study period. For 24-hr urine collection periods, urine was collected via an indwelling Foley catheter attached to a disposable closed collection system. After placement of the catheter the bladder was completely emptied. Urine was then evacuated at 4-hour intervals by means of a 1-way valve, volume was measured, and aliquots frozen at -20°C until later analysis. Ten percent (10%) of the urine collected from each of the 4-hr time points was pooled to create a representative 24-hr pooled sample. Single spot urine samples were also collected from the six mares on three different days using rigid mare urine collection catheters. Urine protein and creatinine were measured by standard methodology.

All results obtained from horses and ponies were sufficiently similar such that the 12 animals were evaluated as a single group. 24-hr urine protein excretion ranged from 403.7 to 3144.2 mg (mean 1451.2 mg; median 1513.5 mg; SD 771.2 mg). UPC in pooled samples showed excellent correlation to 24-hour total protein excretion values (R2=0.913). UPC values measured from aliquots of each of the 4-hr time points likewise showed excellent correlation with 24-hr protein excretion, and minimal change over the 24-hr period, with values fluctuating maximally by 156.8% from the pooled UPC value. UPC results from urine collected on different days likewise remained relatively consistent, with results changing maximally by 170.1% from the pooled UPC value; however, all values remained within normal values reported in other species.

This study provides a preliminary reference range for 24-hr urine protein excretion in equids, and establishes the reliability of UPC as a clinical estimator of 24-hr protein excretion. Future studies will increase the power of the results reported here, and investigate the use of the UPC as a diagnostic test and prognostic indicator in various systemic inflammatory diseases of equids.

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Benjamin Uberti

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