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Fundamentals of Urinalysis
Fundamentals of Urinalysis
Definition & Importance: A critical laboratory test and part of a minimum database used to document urinary tract and systemic diseases (e.g., liver failure, hemolysis).
Definition & Importance: A critical laboratory test and part of a minimum database used to document urinary tract and systemic diseases (e.g., liver failure, hemolysis).
• Collection Methods: Cystocentesis, urethral catheterization, or voiding.
• Collection Methods: Cystocentesis, urethral catheterization, or voiding.
• Sample Handling:
• Sample Handling:
◦ Evaluate within 30 minutes or refrigerate for up to 24 hours (note: refrigeration may cause crystal precipitation).
◦ Evaluate within 30 minutes or refrigerate for up to 24 hours (note: refrigeration may cause crystal precipitation).
◦ Preservation: If cytologic evaluation is delayed, add a few drops of 10% formalin; however, this makes standard Romanowsky stains unsuitable.
◦ Preservation: If cytologic evaluation is delayed, add a few drops of 10% formalin; however, this makes standard Romanowsky stains unsuitable.
◦ Samples must be at room temperature for accurate SG and chemical analysis
◦ Samples must be at room temperature for accurate SG and chemical analysis
Physical Appearance (Gross Examination)
Physical Appearance (Gross Examination)
Color:
Color:
◦ Normal: Transparent yellow or amber.
◦ Normal: Transparent yellow or amber.
◦ Abnormal: Caused by endogenous or exogenous pigments; discolored urine can cause false-positive reagent strip results.
◦ Abnormal: Caused by endogenous or exogenous pigments; discolored urine can cause false-positive reagent strip results.
Clarity: Typically clear; turbidity is caused by crystalluria, hematuria, pyuria, lipiduria, mucus, or pigmenturia.
Clarity: Typically clear; turbidity is caused by crystalluria, hematuria, pyuria, lipiduria, mucus, or pigmenturia.
Odor:
Odor:
◦ Normal: Slight ammonia smell; pungent in cats and goats.
◦ Normal: Slight ammonia smell; pungent in cats and goats.
◦ Abnormal: Strong ammonia odor suggests urease-producing bacteria.
◦ Abnormal: Strong ammonia odor suggests urease-producing bacteria.
Urine Chemistries
Urine Chemistries
• Specific Gravity (SG):
• Specific Gravity (SG):
◦ Measurement: Use a refractometer calibrated for veterinary samples (special scale for cats).
◦ Measurement: Use a refractometer calibrated for veterinary samples (special scale for cats).
◦ Interpretation: Highly variable but normally ≥1.015; Hypersthenuric (>1.025–1.040) in dehydrated animals; Dilute (<1.010) can indicate renal failure, diabetes insipidus, or hyperadrenocorticism.
◦ Interpretation: Highly variable but normally ≥1.015; Hypersthenuric (>1.025–1.040) in dehydrated animals; Dilute (<1.010) can indicate renal failure, diabetes insipidus, or hyperadrenocorticism.
• Reagent Strips (Dipsticks):
• Reagent Strips (Dipsticks):
◦ Valid Tests: pH, protein, glucose, ketones, bilirubin, urobilinogen, and occult blood.
◦ Valid Tests: pH, protein, glucose, ketones, bilirubin, urobilinogen, and occult blood.
◦ Invalid Tests (in animals): Leukocyte esterase, nitrite, and SG test pads.
◦ Invalid Tests (in animals): Leukocyte esterase, nitrite, and SG test pads.
• pH: Typically acidic in dogs/cats and alkaline in horses/ruminants; affects crystal formation (e.g., struvite in alkaline, cystine in acidic).
• pH: Typically acidic in dogs/cats and alkaline in horses/ruminants; affects crystal formation (e.g., struvite in alkaline, cystine in acidic).
• Protein: Primarily detects albumin; must be interpreted alongside SG/pH (trace protein in dilute urine is more significant than in concentrated urine).
• Protein: Primarily detects albumin; must be interpreted alongside SG/pH (trace protein in dilute urine is more significant than in concentrated urine).
◦ UP:UC Ratio: Used to quantitate proteinuria when sediment is inactive (>0.5:1 in dogs and >0.4:1 in cats is abnormal).
◦ UP:UC Ratio: Used to quantitate proteinuria when sediment is inactive (>0.5:1 in dogs and >0.4:1 in cats is abnormal).
• Glucose: Glucosuria occurs when the renal threshold is exceeded (>180 mg/dL in dogs, >240 mg/dL in cats) due to hyperglycemia or tubular defects.
• Glucose: Glucosuria occurs when the renal threshold is exceeded (>180 mg/dL in dogs, >240 mg/dL in cats) due to hyperglycemia or tubular defects.
• Ketones: Detects acetoacetic acid and acetone; associated with ketosis (ruminants), diabetes mellitus (small animals), or starvation.
• Ketones: Detects acetoacetic acid and acetone; associated with ketosis (ruminants), diabetes mellitus (small animals), or starvation.
• Bilirubin/Urobilinogen: Bilirubinuria suggests liver disease or hemolysis; trace amounts are normal in concentrated male dog urine.
• Bilirubin/Urobilinogen: Bilirubinuria suggests liver disease or hemolysis; trace amounts are normal in concentrated male dog urine.
• Occult Blood: Detects RBCs, hemoglobin, and myoglobin; differentiate hemoglobinuria from myoglobinuria by inspecting plasma color (pink/red for hemoglobin).
• Occult Blood: Detects RBCs, hemoglobin, and myoglobin; differentiate hemoglobinuria from myoglobinuria by inspecting plasma color (pink/red for hemoglobin).
Urine Sediment (Microscopic Examination)
Urine Sediment (Microscopic Examination)
• Procedure: Centrifuge 3–5 mL at 1,000–1,500 rpm for 3–5 minutes; examine at 100x and 400x magnification.
• Procedure: Centrifuge 3–5 mL at 1,000–1,500 rpm for 3–5 minutes; examine at 100x and 400x magnification.
• Cells:
• Cells:
◦ RBCs: Normal is <5 RBCs/field; high counts (hematuria) indicate hemorrhage.
◦ RBCs: Normal is <5 RBCs/field; high counts (hematuria) indicate hemorrhage.
◦ WBCs: Normal is <5 WBCs/field; high counts (pyuria) indicate inflammation or infection.
◦ WBCs: Normal is <5 WBCs/field; high counts (pyuria) indicate inflammation or infection.
◦ Epithelial Cells: Transitional (common), Squamous (voided samples), or Neoplastic cells.
◦ Epithelial Cells: Transitional (common), Squamous (voided samples), or Neoplastic cells.
• Casts (Cylindruria): Formed in renal tubules.
• Casts (Cylindruria): Formed in renal tubules.
◦ Types: Hyaline, epithelial, granular, waxy (longstanding), RBC, or WBC casts.
◦ Types: Hyaline, epithelial, granular, waxy (longstanding), RBC, or WBC casts.
◦ Significance: Cellular or high numbers of casts indicate renal damage.
◦ Significance: Cellular or high numbers of casts indicate renal damage.
• Infectious Organisms: Bacteria (rods/cocci), yeast, fungal hyphae, or parasitic ova (e.g., Capillaria plica).
• Infectious Organisms: Bacteria (rods/cocci), yeast, fungal hyphae, or parasitic ova (e.g., Capillaria plica).
• Crystals:
• Crystals:
◦ Struvite: "Coffin-lid" shape; common in dogs/cats.
◦ Struvite: "Coffin-lid" shape; common in dogs/cats.
◦ Calcium Oxalate: Envelope-shaped (dihydrate) or dumb-bell/picket-fence (monohydrate—associated with ethylene glycol toxicity).
◦ Calcium Oxalate: Envelope-shaped (dihydrate) or dumb-bell/picket-fence (monohydrate—associated with ethylene glycol toxicity).
◦ Ammonium urate: Yellow-brown "thorny apple" shape; suggests liver disease or portosystemic shunts.
◦ Ammonium urate: Yellow-brown "thorny apple" shape; suggests liver disease or portosystemic shunts.
◦ Cystine: Six-sided; indicates proximal tubular defects.
◦ Cystine: Six-sided; indicates proximal tubular defects.
• Miscellaneous:
• Miscellaneous:
◦ Lipids: Common in dogs/cats; vary in size and float; not pathologic.
◦ Lipids: Common in dogs/cats; vary in size and float; not pathologic.
◦ Spermatozoa: Normal in intact males.
◦ Spermatozoa: Normal in intact males.
Specialized Testing
Specialized Testing
• Bladder Tumor Antigen Test:
• Bladder Tumor Antigen Test:
◦ Used to screen for transitional cell carcinoma (TCC) in dogs.
◦ Used to screen for transitional cell carcinoma (TCC) in dogs.
◦ Interpretation: High sensitivity (a negative test strongly suggests TCC is not present) but low specificity (infections or hematuria can cause false positives).
◦ Interpretation: High sensitivity (a negative test strongly suggests TCC is not present) but low specificity (infections or hematuria can cause false positives).
Performing a urinalysis is like inspecting a body’s "liquid report card." Just as a report card uses different grades to summarize a student's performance, urinalysis uses physical, chemical, and microscopic data to provide a foundational summary of an animal's internal health, revealing everything from local "plumbing" issues like bladder infections to systemic "engine" failures like liver disease or diabetes.
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