Urinalysis: Components, Factors & Systems

Complete Urinalysis Components:

• Physical characteristics: color, transparency, odor, volume, USG (concentration of solutes).
• Chemical characteristics: protein, glucose, ketones, bilirubin, occult blood, pH.
• Sediment examination.
• Additional tests: culture and sensitivity, urine protein to creatinine ratio, evaluation of urinary calculi/plugs, neoplasia tests.

Factors Affecting Urinalysis Results:

• Exercise, water intake, diseases, drugs, diet & collection method are all factors that can affect urinalysis results. Veterinary technicians should consider these when interpreting findings.

Automated Systems

• Idexx automated analyzers can be used to evaluate urine sediment and show images on a monitor.

Performing Urinalysis

• How soon a UA should be performed, protocols if the urine can't be evaluated in time and what is important to remember after urine has been stored.

Physical Characteristics

• The physical properties of urine include color, transparency/turbidity, odor, volume, and concentration of solutes (urine specific gravity).

Urine Color

• Urine colour should be recorded with a modifier to describe depth such as light or dark.
• Examples of urine colors that can be recorded include dark or light yellow, dark or light brown, dark or light red or colorless.

Normal Urine Color

• Healthy animals have light yellow to amber urine.
• Urine color relates to the urine concentration.
• Urochrome and urobilin are what gives urine its yellow color.
• Color is determined on a well mixed sample.
• The first urine sample of the day in a healthy dog is likely concentrated and more deeply colored.

Rabbit Urine Color

• Ranges from yellow to white, but may turn orange-red-brown due to porphyrin pigments, which is dependent on diet.

Horse Urine Color

• Usually yellow, but turns brown upon standing due to oxidation.

Porphyrin-like Molecules

• Urine turns red after exposure to the air where there are porphyrin-like molecules (easily seen in snow).

Abnormal Urine Color

• Pink-red and red-brown urine can indicate any of hematuria, hemoglobinuria, myoglobinuria.
• Hematuria's urine will be cloudy, but supernatant clears after centrifugation with an RBC pellet present.
• Hemoglobinuria's supernatant will remain red to red-brown after centrifugation with no RBC pellet present
• Myoglobinuria's supernatant remains red-brown to brown with no sediment.

Hemoglobinemia & Hemoglobinuria

• Hemoglobinemia causes reddish discoloration of the blood plasma. This results in hemoglobinuria in the urine sample.

Myoglobinuria

• Red-brown to brown urine suggests myoglobinuria.
• It is caused by severe muscle damage, such as equine exertional rhabdomyolysis (AKA azoturia, Monday morning disease, tying up).
• Color alone can't diagnose myoglobinuria.

Other Abnormal Urine Colors

• Yellow to orange urine may indicate highly concentrated urine or bilirubinuria.

Urine Transparency Terms

• Clear, slightly cloudy, cloudy, and turbid/opaque.
• Transparency should be determined on a well-mixed sample.

Transparency Expectations

• Fresh urine is normally clear.
• Exceptions include horses (calcium carbonate crystals and mucus), rabbits/hamster/guinea pigs (calcium salts). Feline urine can also be slightly cloudy due to fat.
• Urine may become cloudy because of crystal formation or increased bacteria.

Causes of Turbid Urine

• Cells, cellular debris, crystals, bacteria, casts, mucus, sperm, lipids or feces.

Urine Odor

• It usually adds little diagnostic information.
• Ammonia odor may be caused by bacterial urease action.
• Acetone (fruity/sweet) odor suggests ketosis in cows, pregnancy toxemia in ewes, and diabetic ketoacidosis in dogs and cats.
• A putrid odor suggests bacterial degradation of protein.
• Intact male cats, pigs, goats, and mice have stronger urine.
• Medications and diet may affect odor.

Factors Affecting Urine Volume

• Fluid intake, fluid loss, diet, activity, size of animal, species, and environmental conditions.

Normal Urine Volumes

• Cat: 10-20 ml/kg/day
• Cow: 17-45 ml/kg/day
• Dog: 20-100 ml/kg/day
• Goat: 10-40 ml/kg/day
• Horse: 3-18 ml/kg/day
• Pig: 5-30 ml/kg/day
• Sheep: 10-40 ml/kg/day
• Metabolism cages, catheterization, and collection bags measure 24-hour urine output.

Standardized Volume for Urinalysis

• Many human labs use 10 ml as the standard volume.
• Some veterinary labs use a standard volume of 3 ml to 6 ml of urine for analysis.

Terms for Urine Production Abnormalities

• Polyuria: Increased urine production or output, often with polydipsia (increased drinking), as seen in untreated diabetes mellitus or hyperadrenocorticism.
• Pollakiuria: Frequent urination.
• Oliguria: Decreased urine output or production, e.g., shock, dehydration.
• Anuria: No urine output or production, e.g., urethral obstruction.
• Incontinence: Dribbling of urine.
• Dysuria: Difficult or painful urination.
• Stranguria: Slow and painful urination, sometimes with tenesmus.

Urine Specific Gravity

• Urine specific gravity, sometimes shortened to USG, measures the ratio of the density of urine to the density of an equal volume of distilled water.
• This measures the concentration of the solutes in a urine sample.
• It reflects the ability of the kidneys to concentrate or dilute urine compared with the specific gravity of plasma.
• It measures the renal tubules' ability to concentrate or dilute filtrates from the glomerulus to maintain water and osmotic balance.
• It is evaluated with serum creatinine, SDMA, and BUN, as well as the hydration status of the patient.

Measurement Methods

• Refractometer: Measures density of urine compared to density of water using 2-3 drops of urine which is an ideal method for USG.

Refractometer Usage

• A solute bends light as it passes through urine, in proportion to the solute concentration.
• If the SG is off the internal scale, dilute the urine sample with an equal volume of distilled water, read the SG again, and multiply the last two digits of the value by 2.
• The refractivity of urine differs in cats, rabbits, and guinea pigs compared to dogs, large animals, and humans.

Refractometer Usage Notes

• Specific scales should be used whenever possible.
• Human refractometers will elevate cat readings, while those of rabbits and guinea pigs will be lowered.
• Large amounts of glucose or protein can falsely increase USG.
• For quality control use distilled water to check zero setting (1.000) and a known control such as 5% NaCl solution (1.022).
• Adjust it according to the manufacturer's instructions.

Urine Specific Gravity Terminology

• Sthen means strength.
• Iso means the same as.
• Hypo means less than.
• Hyper means greater than.

Urine Specific Gravity Levels and Meanings:

• USG <1.008 (Hyposthenuria): Filtrate/urine is being diluted below the SG of plasma by the renal tubules.
• USG 1.008 – 1.012 (Isosthenuria): The SG of the glomerular filtrate/urine and plasma are the same; the filtrate/urine has not been concentrated or diluted in the renal tubules.
• USG >1.012 (Hypersthenuria): Filtrate/urine is being concentrated above the SG of plasma by renal tubules.

Hypersthenuria Specifics

• ≥1.030 in dogs, ≥1.035 in cats, ≥ 1.020 in horses and ruminants.
• Urine is appropriately concentrated
• There is an appropriate renal response to antidiuretic hormone
• ≥1/3 of the total nephron population is functional and renal medullary hypertonicity is present

Concentrated Minimums

• Minimal concentrations range from >1.012 – <1.030 in dogs, >1.012 - <1.035 in cats, and 1.012 - <1.020 in horses and ruminants.
• Urine is dilute compared with plasma and may be normal in a well-hydrated patient.
• This can be inappropriate in the face of dehydration or azotemia

Specific Gravity Ranges

• 1.008–1.012 is the range, in dogs and cats, where the urine has not been concetrated or diluted, as the specific gravity is similar to plasma.
• There may be a normal response to increased fluid intake.
• Specific to be, it should be inappropriate in the face of dehydration or azotemia.

Hyposthenuria Specifics

• <1.008 in dogs and cats.
• Urine is dilute compared with plasma, ≥1/3 of the total nephron population is functional.
• This is inappropriate in the face of dehydration or azotemia

Normal Ranges

• Urine specific gravity ranges from 1.001 – 1.065 in normal animals and up to 1.085 in cats.
• Values fluctuate day-to-day and within a day.

Expectations for Adequate Concentrating Ability:

• Dogs have a random USG of 1.030 or higher.
• Cats have a random USG of 1.035 or higher.
• Horses and cows have a random USG of 1.020 or higher.

Urine Specific Gravity Interpretations

• If there is low USG and azotemia (increased BUN, creatinine and SDMA) suspect renal failure.
• Important to review hydration status when interpreting USG.
• Most neonates (except calves) don't have efficient concentrating mechanisms.