Urinalysis is an essential test for evaluating kidney function. Whenever blood is collected for a chemistry profile, a urine sample should be obtained whenever possible (especially on the initial sampling). Changes in renal parameters cannot be interpreted without knowledge of the urine results. For example, a high BUN and creatinine (azotemia) in a dehydrated patient with a concentrated urine (urine specific gravity > 1.030 in a dog) is compatible with a pre-renal azotemia, whereas azotemia in a dehydrated dog with a USG of 1.010 indicates a renal azotemia. Urine should be collected into sterile glass red-top containers for all our tests. Plastic tubes should be avoided, because we have found that they often contain microscopic crystalline material that can interfere with the urine sediment exam.

We offer routine urinalysis, protein:creatinine ratios, and certain individual urine chemistry tests. Fractional excretion of electrolytes can be calculated by measuring the concentration of electrolytes and creatinine in serum and urine. Urinary excretion of electrolytes and certain enzymes, e.g. GGT, can indicate renal disease, e.g. Fanconi's syndrome and aminoglycoside toxicity (urinary GGT).

To view our reports for certain tests below and to obtain more information about the individual components of each test, click on the highlighted test name below.

Urine Osmolality

Urine osmolality is measured by freezing point depression in our laboratory. Osmolality is affected by the number of osmotically active particles in solution and is unaffected by their molecular weight and size. For this reason, osmolality is superior to specific gravity, which is affected by particle weight and size. Isosthenuric urine has an osmolality similar to plasma, approximately 300 to 320 mOsm/kg. Urine osmolality is useful for evaluating urine concentrating ability, for example in water deprivation tests, and is more accurate than measurement of urine specific gravity in this regard.

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.

Urine Uric Acid

This is used to detect excessive urate excretion in breeds, such as Dalmatians, and to monitor response to therapy with allopurinol. Dalmatians excrete up to 400 to 600 mg uric acid per day in their urine, compared to non-Dalmation dogs, which excrete less than 100 mg uric acid per day in urine.

The best method for measuring urinary urate excretion is from a 24-hour urine collection, as recent studies have shown that a single urine uric acid to creatinine ratio does not correlate well to 24-hour urinary uric acid excretion. In addition, the amount of uric acid excreted in urine is dependent on diet (higher on meat-based diets). However, measurement of 24-hour excretion of uric acid in the urine is cumbersome and impractical and most people use urine uric acid to creatinine ratios for monitoring therapy. Guidelines in the literature for uric acid/creatinine ratios in urine are shown below:

Care must be taken when submitting urine samples for measurement of uric acid. Uric acid precipitates rapidly when urine is cooled, so the sample must be resuspended and a well-mixed aliquot provided to the laboratory, to prevent falsely decreased values due to precipitation (ideally, the urine should be submitted in the original container it was collected into).