urine 3

• Veterinary Lab Techniques 2: Urine & Microbiology.
• Urine Sediment Urinalysis, Winter 2025

Learning Outcomes

• Prepare urine sediment for evaluation using wet mounts and air-dried smears.
• Identify epithelial cells, erythrocytes, leukocytes, and casts in urine sediment.
• Apply knowledge to case studies.

Overview of Urine Sediment Examination

• Examinie urine sediment microscopically after evaluating physical and chemical properties.
• Urinalysis is important, providing specific information for a definitive diagnosis.
• Centrifuge urine soon after collection to prevent changes in sediment composition.

Potential Findings in Urine Sediment

• Casts.
• Bacterial rods.
• Erythrocytes.
• Leukocytes.
• Epithelial cells.
• Crystals.

Centrifugation Process

• Thoroughly mix the urine sample before centrifugation.
• Samples must be at room temperature and fresh.
• Load urine into conical-tipped centrifuge tubes.
• Cap the specimen to prevent aerosol formation.
• Balance the centrifuge.
• Use the RPM and time recommended by the centrifuge manufacturer, e.g. 1000 - 3000 RPM for 5-6 minutes (micro methods use very small urine amounts).
• Remove most of the supernatant, leaving a small amount (0.2 - 0.5 ml) to resuspend the sediment by tapping the tube bottom gently.
• Maintain a consistent amount of supernatant each time.

Preparing Slides

• Transfer a small amount of resuspended sediment to a glass slide using a disposable pipette.
• Place a coverslip on top of the wet mount.

Preparing Stained Slides

• Add 1 or 2 drops of Sedistain or NMB stain, depending on the amount of sediment, to sediment in the centrifuge tube.
• Sedi-Stain® is Sternheimer-Malbin stain.
• New Methylene Blue (NMB) stain can also be used.
• Urine sediment can also be made into a line smear, air-dried quickly and stained with Diff Quik.
• Line smears are Ideal for evaluating cell types, including neoplastic cells.
• Line smears are not suitable for viewing crystals or casts.

Guidelines for Wet Mount Slides

• Lower the condenser, adjust iris diaphragm to increase contrast
• Scan first with 10x objective (low-power field [LPF]) and later 40x objective (high-power field [HPF]).
• Estimate crystal and cast numbers as the average number per LPF (10x).
• Estimate cells as average number per HPF (40x).
• Score sperm and bacteria as none, few, moderate number, or many per HPF.
• Use an air-dried smear stained with Diff Quik to accurately identify bacteria, especially bacteria that have been phagocytized, and use the 100x objective for this purpose (not a wet mount).

Urine Sediment Components

• Method of collection impacts the type and amount of sediment.
• Methods causing iatrogenic hemorrhage and blood cells in sediment: Cystocentesis, catheterization, manual expression.
• Methods contributing to squamous epithelial cells and bacteria: Free flow (voided), MAYBE catheterization (placement).
• Epithelial cells.
• Erythrocytes.
• Leukocytes.
• Casts.
• Mucus.
• Fat.
• Bacteria.
• Sperm.
• Parasites and parasite eggs.
• Fungi.
• Crystals.

Epithelial Cells Overview

• Types are squamous, transitional, and renal epithelial cells.

Squamous Epithelial Cells

• Large cells.
• Irregular angular margins.
• Small central nucleus.
• The nucleus is sometimes not visible.
• They originate from the distal urethra, vagina, or prepuce.

Transitional Epithelial Cells

• Vary in size and shape; oval, spindle-shaped, or caudate (tail present).
• Originate from the proximal urethra, bladder, ureter, or renal pelvis.
• May occur in groups, especially if a catheter is used.
• Normal urine should have less than 5/HPF.
• Large numbers with RBCs and WBCs indicate cystitis.
• They are approximately 2-4 times larger than WBCs.
• They are the most common epithelial cell observed in urine and in the urinary tract.

Renal Epithelial Cells

• Small, round cells.
• Large nucleus (usually eccentric).
• Slightly larger than leukocytes.
• May be difficult to differentiate from WBCs or transitional epithelial cells.
• Originate from the renal tubules.
• Rarely seen.
• A large number equals renal tubule disease.

Neoplastic Cells

• Transitional cell carcinoma (TCC) is more common in dogs.
• The bladder is the most common site but it can occur in other parts of the urinary tract.
• Suspect genetic predisposition.
• Clinical signs include hematuria, stranguria, and pollakiuria.
• Diagnosis via tissue biopsy or tumor cells in sediment (cytology, latex agglutination test, Cadet BRAF mutation detection assay).

Erythrocytes

• Round, slightly refractive.
• Crenation occurs in concentrated urine.
• Swelling occurs in dilute urine.
• Ghost cells occur in dilute urine.
• May resemble fat droplets but vary in size & float to different planes of focus.
• More than 4-5 RBCs per HPF indicates hematuria.

Leukocytes

• Normally very few in urine sediment.
• Mostly neutrophils - round, granular, larger than RBCs, and smaller than epithelial cells.
• More than 5 per HPF is abnormal and indicates pyuria (septic or non-septic).
• Leukocytes may be associated with bacteria.
• A stained smear is needed to identify intracellular bacteria.
• Urine culture is recommended.

Casts

• Elongated structures composed mainly of a matrix of mucoprotein (Tamm-Horsfall protein).
• Cells may stick to protein and become embedded in the cast.
• Casts are formed in renal tubules.
• Their appearance depends on the time they have remained in tubules.
• Few to no casts are seen in healthy animals, and when they are usually hyaline or finely granular.
• With renal tubular injury, epithelial cells slough into the lumen of the renal tubules and are caught up within a mucoprotein matrix made from Tamm-Horsfall protein (hyaline cast), forming a cellular cast.
• Over time, the epithelial cells degenerate and can no longer be recognized as cells within the hyaline matrix, forming coarsely granular, then finely granular casts.
• Waxy casts are the final step in the formation of casts and usually indicate chronic tubular disease.
• Cast formation prerequisites include acidic urine, high urine salt concentration, reduced tubular flow rate, and the presence of a mucoprotein matrix.
• Casts may dissolve in alkaline urine, so they should be evaluated ASAP.
• Structures present in the tubule during formation may be embedded in the cast matrix.
• Casts indicate some tubular change (renal irritation, inflammation, or degeneration) but do not correlate with severity.
• A few hyaline or finely granular casts per LPF may be seen in healthy animals.
• Cellular casts are usually significant.
• They are discharged intermittently and may not be seen in just one urinalysis.
• Absence of casts does not rule out renal disease.
• Renal epithelium can regenerate if the cause of the injury is eliminated.

Types of Casts

• Hyaline.
• Epithelial.
• Leukocyte.
• Erythrocyte.
• Granular.
• Waxy.
• Fatty.

Hyaline Casts

• Colourless, homogenous, and semi-transparent.
• Cylindrical with rounded ends.
• Composed of mucoprotein.
• Do not contain cells.
• Require reduced light to see.
• A few may be seen in healthy animals.

Epithelial Casts

• Hyaline casts that contain many renal epithelial cells which have not disintegrated.
• Difficult to distinguish from WBC casts.
• Seen in diseases that damage tubular epithelium.

Leukocyte Casts

• Indicate inflammation (e.g., pyelonephritis).
• Usually composed of neutrophils.
• Difficult to distinguish from renal epithelial casts.
• Look for free leukocytes.
• Decompose to form granular, then waxy casts.

Erythrocyte Casts

• Indicate hemorrhage into tubules or inflammation.
• Fragile.
• Are hyaline casts with RBCs.
• Rare in dogs and cats.

Granular Casts

• Usually a stage in the degeneration of cellular casts.
• Contain granules from the disintegration of cells and plasma proteins.
• Start as coarse granules (often dark brown) and degenerate to fine granules (pale yellow).
• Low numbers are occasionally seen in healthy urine.
• High numbers indicate tubulointerstitial disorder or severe renal disease.

Waxy Casts

• Grey to colourless and highly refractile.
• Final stage of cellular cast formation.
• Indicate more chronic tubular injury.
• Broader and more solid than hyaline casts.
• Usually have broken off square ends.
• Formed in collecting tubules.
• Can be Highly convoluted.

Fatty Casts

• Seen in diseases of the renal tubules.
• Contain fat droplets which are very refractive and vary in size.
• Lipid comes from degenerating tubular epithelial cells.
• Most frequently seen in cats with renal disease due to the high lipid content of tubular epithelial cells in this species.