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Clinical Pathology


Urine Protein to Creatinine Ratio

Because the protein in urine is generally quite low (< 1 g/dL), it cannot be measured using the Biuret procedure that is used for measuring total protein in serum or plasma. A more sensitive technique is required. On the Mod P, we measure protein in urine (and CSF) with benzethonium chloride, which precipitates the protein and increases the turbidity of the sample. The turbidity is proportional to the protein concentration. This technique is very sensitive and can yield accurate results in samples with very low protein concentrations (< 20 mg/dL). Creatinine in urine is measured using our standard rate-blanked creatinine procedure.

The protein-creatinine ration (UP:UC) is used to provide an estimate of the amount of protein lost in the urine. The urine protein to creatinine ratio on random mid-day urine samples correlates well to 24-hour urine collection, for quantitating urinary protein loss. The degree of proteinuria yields useful information on the source of protein loss; namely losses of large amounts of protein (with high urine protein to creatinine ratios) is due to glomerular, and not tubular, disease. Urine protein to creatinine ratios should only be performed on urine samples with evidence of excess protein (with consideration of the USG) and no evidence of cystitis. For example, there is no point in performing a urine protein to creatinine ratio in a patient with a USG of 1.035 and trace protein on the dipstick. Inflammatory conditions in the urinary tract will increase protein and negate the usefulness of the ratio for determining the source of protein loss.

 

Interpretation of UP:UC in dogs/cats

Dogs

In healthy dogs, the urine protein to creatinine ratio (UP:UC) is usually <0.5.  Values between 0.5-1.0 in non-azotemic dogs are considered equivocal and continued monitoring for progression is recommended.  Values >1.0 in non-azotemic dogs are abnormal and diagnostic evaluation is warranted.  Glomerular proteinuria is usually associated with UP:UC >=2.0.  Therapeutic intervention is recommended for azotemic dogs with UP:UC >=0.5.  These figures are only valid for urine samples with inactive sediments.

Cats

In healthy cats, the urine protein to creatinine ratio (UP:UC) is usually <0.5.  Values between 0.5-1.0 in non-azotemic cats are considered equivocal and continued monitoring for progression is recommended.  Note that some healthy male cats can have UP:UC values within this range (up to 0.6).  Values >1.0 in non-azotemic cats are abnormal and diagnostic evaluation is warranted. Glomerular proteinuria is usually associated with UP:UC >=2.0.  Therapeutic intervention is recommended for azotemic cats with UP:UC >=0.4.  These figures are only valid for urine samples with inactive sediments.