urinary2

• Urinalysis evaluates urine's physical and chemical characteristics, sediment, and can include additional tests such as cultures and neoplasia tests
• Factors like exercise, water intake, diseases, drugs, diet, and collection method affect urinalysis results

Physical Characteristics

• Physical characteristics include color, transparency/turbidity, odor, volume, and concentration of solutes

Urine Color

• Record urine color with a modifier for depth (dark or light)
• Examples of urine colors include dark or light yellow, dark or light brown, dark or light red, and colorless
• Most healthy animals have light yellow to amber urine
• Urine color is related to concentration
• Urochrome and urobilin impart yellow color
• Color is determined on a well mixed sample
• Rabbit urine color varies from yellow to white but may turn orange-red-brown, depending on diet
• Horse urine is yellow but often browns upon standing due to oxidation
• Porphyrin-like molecules in urine will turn it red after exposure to air

Abnormal Urine Color

• Pink-red and red-brown urine indicates hematuria, hemoglobinuria, or myoglobinuria
• Hematuria presents as cloudy urine with a red blood cell (RBC) pellet post-centrifugation
• Hemoglobinuria presents as red to red-brown supernatant after centrifugation, without an RBC pellet
• Myoglobinuria presents as red-brown to brown supernatant with no sediment

Hemoglobinemia

• Reddish discoloration of blood plasma indicates hemoglobinemia, which can result in hemoglobinuria

Myoglobinuria

• Red-brown to brown urine suggests myoglobinuria
• Myoglobinuria is caused by severe muscle damage.
• Equine exertional rhabdomyolysis may be seen in this condition

Other Urine Colours

• Yellow to orange urine indicates concentrated urine or bilirubinuria

Urine Transparency

• Transparency terms include clear, slightly cloudy, cloudy, and turbid/opaque
• Transparency is determined on a well mixed sample
• Normal urine is clear when fresh
• Exceptions to clear urine include horses (calcium carbonate crystals and mucus), rabbits, hamsters and guinea pigs (calcium salts), and feline urine (fat)
• Standing samples may turn cloudy due to crystal formation or bacterial increase

Causes of Turbid Urine

• Causes include cells, cellular debris, crystals, bacteria, casts, mucus, sperm, lipids, and feces

Urine Odour

• Urine odour adds little diagnostic information
• Ammonia is formed by the action of bacterial urease
• Acetone (fruity/sweet) odour suggests ketosis
• Putrid odour suggests bacterial degradation of protein
• Intact male cats, pigs, goats, and mice have strong urine
• Medications and diet may affect odour

Urine Volume

• Factors affecting the amount of urine produced include fluid intake, fluid loss (e.g. vomiting, diarrhea), diet (e.g. wet food versus dry food), activity, size of animal, species, and environmental conditions
• Cat normal urine volume is 10-20 ml/kg/day
• Cow normal urine volume is 17-45 ml/kg/day
• Dog normal urine volume is 20-100 ml/kg/day
• Goat normal urine volume is 10-40 ml/kg/day
• Horse normal urine volume is 3-18 ml/kg/day
• Pig normal urine volume is 5-30 ml/kg/day
• Sheep normal urine volume is 10-40 ml/kg/day
• Metabolism cages, catheterization and collection bags measure 24-hour urine output
• Human labs use 10 ml as the standard volume
• Some veterinary labs use 3-6 ml of urine for analysis

Terminology

• Polyuria is increased urine production, often with polydipsia (increased drinking)
• Pollakiuria is frequent urination
• Oliguria is decreased urine output
• Anuria is no urine output
• Incontinence is dribbling of urine
• Dysuria is difficult or painful urination
• Stranguria is slow and painful urination with tenesmus

Urine Specific Gravity

• Specific gravity (USG) measures the ratio of urine density to distilled water density
• USG indicates the concentration of solutes in urine
• USG reflects kidney's ability to concentrate or dilute urine
• USG measures renal tubules' ability to concentrate or dilute filtrates
• Measured with serum creatinine, SDMA, BUN, and patient hydration status
• Refractometers measure the density of urine compared to the density of water, only requiring 2-3 drops of urine
• Urinometers require at least 10 ml of urine and must be calibrated for temperature
• Reagent strips are not reliable

Refractometers

• Solutes bend the light passing through urine
• Dilute samples with a high SG to read

Refractometer usage

• Use species-specific internal scales when possible

• Human refractometers will elevate cat USG

• Large amounts of glucose or protein will falsely increase USG

Refractometer Quality Control

• Use distilled water to check zero setting (1.000) and 5% NaCl solution (1.022) as a known control
• Adjust according to manufacturer's instructions

Terms

• "sthen" means strength
• "Iso" means the same as
• "Hypo" means less than
• "Hyper" means greater than

Specific Gravity ranges

• In hyposthenuria (USG <1.008), urine is diluted below plasma SG by the renal tubules
• In isosthenuria (USG 1.008 - 1.012), glomerular filtrate/urine and plasma have the same SG, indicating neither concentration nor dilution by the renal tubules
• In hypersthenuria (USG>1.012), filtrate/urine is concentrated above plasma SG by renal tubules

Hypersthenuria Levels

• Urine is concentrated
• Appropriate renal response to antidiuretic hormone
• Greater than or equal to 1/3 of the total nephron population is functional and with renal medullary hypertonicity
• Dogs: ≥1.030
• Cats: ≥1.035
• Horses and ruminants: ≥1.020

Range on Minimal Concentration

• Dogs: >1.012 - <1.030
• Cats: >1.012 - <1.035
• Horses and ruminants: 1.012 -

Specific Gravity Considerations

• Inappropriately dilute urine compared with plasma
• May be normal in a well-hydrated dog or cat.
• Inappropriate in the face of dehydration or azotemia

Isosthenuria details

• The specific gravity is similar to that of plasma
• May be normal response to recent water intake or fluid therapy
• Inappropriate in the face of dehydration or azotemia

Hyposthenuria details

• Greater or equal to 1/3 of the total nephron population is functional
• Inappropriate in the face of dehydration or azotemia

Specific Gravity in animals

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

Low USG

• Low USG and azotemia indicate renal failure

USG Considerations

• Knowledge of hydration status is important when interpreting USG
• Most neonates (except for calves) do not have efficient concentrating mechanisms