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Urinary Tract Inflammation Has a Variable Effect on Urine Albumin Concentrations

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SUMMARY:

• Historically, lower urinary tract disease (LUTD) has been thought to be a primary cause of proteinuria.
• This study shows 65% of dogs with LUTD were negative for microalbuminuria.
• When both microalbuminuria and LUTD are present, dogs should be re-tested after successful treatment of LUTD.

Urinary tract inflammation is thought to be a cause of proteinuria in dogs. In one study of urinary tract inflammation experimentally induced by either cystotomy or infection, all dogs developed proteinuria with urine protein:creatinine ratios >1.5. However, when proteinuria was evaluated in dogs presenting to a veterinary teaching hospital that had abnormal urine microscopic examinations, 66% had qualitative proteinuria (sulfosalicylic acid) but only 35% had urine protein:creatinine ratios >1.0. Methods used in these studies measure not only urine albumin (UAlb) but also urine globulin. A method to quantify UAlb in dogs has recently become available. The purpose of this study was to determine the effect of urinary tract inflammation on UAlb concentrations.

Urine samples were obtained from dogs presenting for routine health screening, elective procedures and evaluation of health problems at the Veterinary Teaching Hospitals at Colorado State University and North Carolina State University and from dogs in a colony of soft coated wheaten terriers (SCWT) and SCWT x beagle crosses (SCWTx). SCWT and SCWTx with known protein-losing nephropathy were excluded. UAlb concentrations were measured in samples with pyuria (>5 WBC/hpf) using a canine albumin specific competitive ELISA.

Of 70 samples with pyuria, 40 (57%) had negligible UAlb concentrations (<1 mg/dl); whereas microalbuminuria (1-30 mg/dl) and macroalbuminuria (>30 mg/dl) were present in 25 (36%) and 5 (7%) of the samples respectively. Bacteriuria (trace to 4+) and hematuria (>5 RBC/hpf ) were concurrent microscopic abnormalities in 26 and 17 dogs, respectively. UAlb concentrations were significantly higher in urine samples with bacteriuria (2.5, 0.21, 7.6; median, 25th, 75th percentile) when compared with samples without bacteriuria (0.26, 0.19, 2.3; p<0.05, Wilcoxon test). A significant difference was not detected between dogs with and without hematuria.

Albuminuria is associated with pyuria in some dogs and is more common in dogs with bacteriuria. However, a large percentage of dogs with pyuria do not have albuminuria. More study is needed to determine the sources of pyuria that contribute to albuminuria.

Reproduced with permission of the Journal of Veterinary Internal Medicine.