Histology and Urinalysis Quiz

Urinalysis Benchtop Reference Guide

• This guide provides an illustrated reference for cell morphology in urinalysis
• It covers various components, including urinary cells, casts, and crystals

Urinary Cells

• Erythrocyte:

  • Appearance: Pale, yellow-orange discs; in hypotonic solutions, they appear colorless "ghost" shapes. In hypertonic solutions, they appear crenated (irregular surfaces).
  • Size: 7-8 µm
  • Special Features: Presence of a few RBCs (<3/high-power field) is normal; increased numbers indicate kidney/urinary tract disease or menstrual blood contamination. Must differentiate from oil droplets (highly refractile) and yeast cells (smaller, oval to round, budding).

• Erythrocyte, Dysmorphic:

  • Appearance: Variable; similar to normal erythrocytes, but with irregular cytoplasmic boundaries/blebs (sometime appearing as "Mickey Mouse ears"), altered central pallor (codocytes, stomatocytes, acanthocytes, etc.)
  • Size: 7-8 µm
  • Special Features: Loss of limiting membrane, indicative of glomerular bleeding (like glomerulonephritis)

• Leukocyte (Neutrophil, Eosinophil, Lymphocyte):

  • Appearance: Colorless on unstained slides; neutrophils show cytoplasmic granulation with nuclear segmentation (though degeneration may result in a single nucleus); eosinophils are larger than neutrophils and lymphocytes are smallest; lymphocytes have agranular cytoplasm.
  • Size: -Neutrophil: 12 µm
    • Eosinophil: 10-15 µm
    • Lymphocyte: 7-15 µm
  • Special Features: Less than five neutrophils/high-power field may be normal; increased neutrophils associated with infection; >1% eosinophils associated with interstitial nephritis; rare lymphocytes can increase after renal transplantation.

• Monocyte/Macrophage:

  • Appearance: Variable; ranging from monocyte morphology to activated macrophages, with abundant cytoplasm that may appear frayed or contain vacuoles, granules, or ingested debris; lobulated band-like/bean-shaped nucleus.
  • Size: 14-30 µm (larger than neutrophils)
  • Special Features: Ingested material (lipid, etc.) may be present; often seen in chronic inflammation and radiation therapy.

• Renal Tubular Epithelial (RTE) Cell:

  • Appearance: Polyhedral shape, granular cytoplasm, and often eccentric nucleus; surface may be frayed; microvilli present.
  • Size: 20-35 µm
  • Special Features: Line kidney nephron; their presence indicates renal tubular damage (acute tubular necrosis, viral infection, or renal transplant rejection); differentiate from neutrophils, mononuclear leukocytes, and transitional epithelial cells. Evaluate for viral inclusion bodies. Fat droplets ("oval fat bodies") characteristically show "Maltese cross" on polarization; use Oil Red O or Sudan stain for confirming lipid presence; Prussian blue stain for iron/hemosiderin confirmation.

• Spermatozoa:

  • Appearance: Sperm head smaller and narrower than erythrocyte; a long slender tail, which may detach.
  • Size: 2-6 µm (head); 40-60 µm (tail)
  • Special Features: Found in men with retrograde ejaculation, post-prostatectomy, or samples collected soon after ejaculation.

• Squamous Epithelial Cell:

  • Appearance: Large cell with abundant cytoplasm; small nucleus; well-defined cell membrane often with occasional curled or folded edges; occasionally binucleated; may show cytoplasmic swelling, frayed borders, or pyknotic nuclei.
  • Size: 30-50 µm (cell size); 10-12 µm (nucleus size)
  • Special Features: Derived from female urethra, distal male urethra, skin, or vaginal mucosa; high numbers indicate contamination.

• Transitional Epithelial Cell (urothelial cell):

  • Appearance: Round to pear shape with central, well-defined, and oval to round nucleus and well-defined cytoplasmic borders; cytoplasmic ratio higher than squamous cells; can occur singly, in pairs, or in clusters; may show cytoplasmic processes ("tadpole cells").
  • Size: Variable (40-200 µm)
  • Special Features: Line renal pelvis, ureters, and bladder (in males, also proximal urethra). Normal constituent of urine; increased numbers associated with infection, renal stones, bladder cancer, and post-catheterization.

Urinary Casts

• Fatty Cast:

  • Appearance: Cylindrical to cigar-shaped, rounded or blunt ends, containing large numbers of spherical, highly refractile fat droplets; may form oval fat bodies.
  • Special Features: Associated with marked proteinuria, acute tubular necrosis or nephrotic syndrome; highly refractile and may show birefringence ("Maltese cross" pattern).

• Cellular Cast (RTE or Neutrophil):

  • Appearance: Contains intact or partially disrupted cells (RTE or neutrophils) in a cylindrical/cigar-shaped matrix.
  • Special Features: Associated with kidney diseases (especially acute tubular necrosis or renal transplant rejection); distinguished from other casts by cellular components.

• Granular Cast:

  • Appearance: Elongated cylinders with smooth margins and evenly dispersed fine to coarse spherical granules.
  • Special Features: Found in normal urine and renal disease, notably stress/strenuous exercise or renal disease; can be confused with hyaline or fatty casts but do not polarize and are refractile.

• Hyaline Cast:

  • Appearance: Colorless, homogeneous, and translucent; cigar-shaped with smooth or finely wrinkled surface, smooth lateral margins, and rounded or tapered ends. Can be coiled or tortuous.
  • Special Features: Common in normal urine and renal diseases and often associated with stress/physiological stress.

• Erythrocyte (Red Blood Cell) Cast:

  • Appearance: Cylindrical to cigar-shaped with rounded ends; uniformly sized red blood cells densely or loosely cover the hyaline or granular matrix. May appear yellow-red. - Special Features: Indicate renal disease such as acute nephritis, glomerular injury, or malignant hypertension.

• Waxy Cast:

  • Appearance: Cylindrical shape, usually broad and stubby; possible serrated, notched, or indented lateral margins; cracked; relatively homogenous, appearing waxy or gel-like.
  • Special Features: Associated with severe or progressive renal disease and acute glomerulonephritis

Urinary Crystals at Acid pH

• Cystine Crystals:

  • Appearance: Clear, colorless, hexagonal form; significant variation in crystal size; weak birefringence when viewed using polarized light.
  • Special Features: Present in large numbers in individuals with cystinosis (congenital, autosomal recessive condition); most common cause of aminoaciduria; diagnosis confirmed via cyanide-nitroprusside test and chromatography/amino acid analysis.

• Sulfonamide Crystals:

  • Appearance: Two types, sulfadiazine (needle-like bundles resembling stacked wheat sheaves, fan shapes, or clumps; have radiating spikes) and sulfamethoxazole (divided or fractured spherical form); dark brown.
  • Special Features: May form renal calculi, particularly in dehydrated individuals but not usually an issue when water-soluble forms are used.

• Uric Acid Crystals:

  • Appearance: Variations in shape (four-sided, wedge, six-sided plates, needles, and stars), usually yellow to brown, strongly birefringent.
  • Special Features: Associated with hyperuricemia, gouty nephropathy, tumor lysis syndrome; differentiates from cystine crystals using birefringence.

• Amorphous Urate Crystals:

  • Appearance: Colorless or red-brown granular aggregates commonly referred to as "brick dust".
  • Special Features: Often found in concentrated urine and correlated with fever or dehydration; differentiated from amorphous phosphates, which occur in alkaline urine.

Urinary Crystals at Neutral or Acid pH

• Bilirubin Crystals:

  • Appearance: Small yellow-brown clusters or clumps resembling spheres with needle-like projections.
  • Special Features: Abnormal in urine and often indicates large amounts of bilirubin and/or bile-stained cells; soluble in various compounds (acetic acid, hydrochloric acid, sodium hydroxide, and acetone).

• Calcium Oxalate Crystals:

  • Appearance: Common dihydrate forms appear as small, colorless octahedrons resembling stars or envelopes (or less common monohydrate forms like dumbbells, ovals, or ellipses). All forms are birefringent.
  • Special Features: Commonly found in diet-rich individuals in oxalic acid (e.g. tomatoes, apples, asparagus).

• Cholesterol Crystals:

  • Appearance: Large, flat, clear, colorless rectangular, or rhomboid plates often with one notched corner; birefringence produces bright hues.
  • Special Features: Rare in fresh urine but can occur with refrigeration; associated with fatty casts, oval fat bodies, and nephrotic syndrome.

• Hippuric Acid Crystals:

  • Appearance: Colorless to pale yellow, frequently appearing as hexagonal prisms, needles or rhombic plates; birefringent.
  • Special Features: Typically found in individuals consuming diets rich in benzoic acid (e.g., vegetables) or associated with acute febrile illness or liver disease.

• Leucine Crystals:

  • Appearance: Highly refractile, brown, spherical crystals with a central nidus and "spoke-like" striations extending to periphery; birefringent but shows a pseudo "Maltese cross" with polarized light.
  • Special Features: Rare, seen in severe liver disease or amino acid metabolism disorders; often appear alongside tyrosine crystals.

• Tyrosine Crystals:

  • Appearance: Silky, fine, colorless to black needles; clumps or sheaves form after refrigeration.
  • Special Features: Rare, associated with leucine crystals in cases of protein metabolism abnormalities like hereditary tyrosinosis or hepatic failure.

Urinary Crystals at Neutral or Alkaline pH

• Ammonium Biurate Crystals:

  • Appearance: Dark yellow or brown spheres with concentric or radial striations, sometimes featuring multiple short to long, irregular projections resembling thorns (commonly referred to as "thorn apples").
  • Special Features: Rare; typically found in alkaline urine that has aged; mimicking crystals; (e.g. sulfamethoxazole, sulfadiazine and leucine).

• Ammonium Magnesium (Triple) Phosphate Crystals:

  • Appearance: Elongated, commonly rectangular, monoclinic prisms with axial symmetry; may assume a fern-like, feathery form as they dissolve; birefringent.
  • Special Features: Commonly associated with bacterial growth.

• Amorphous Phosphate Crystals:

  • Appearance: Fine, colorless or white granules occurring in clumps in alkaline urine.
  • Special Features: Often morphologically identical to amorphous urates; they will not dissolve when heated in a water bath to 60°C.

Organisms

• Bacteria:
  • Appearance: Tiny, colorless, round (cocci) or elongated (bacilli/rods); may occur singly or in chains; clusters
• Yeast/Fungi:
  • Appearance: Oval, colorless, refractile and have single buds; may also exhibit pseudohyphae (branching, non-septated, filamentary structures)
• Miscellaneous/Exogenous
  • Fat Droplet:
    • Appearance: Highly refractile; dark-greenish spherule under low power; clear, globular sphere under high power; show "Maltese cross" when polarized light is used.
  • Fiber (Exogenous)/Fecal Contamination:
    • Appearance: Flat, refractory, colorless; often contain pits, fissures, or cross-striations; can vary greatly in size.
    • Special Feature: Usually originated from clothing, cotton balls, applicator sticks, dressings and disposable diapers.
  • Mucus:
    • Appearance: Translucent; delicate; wavy; intertwined aggregate strands; typically have tapered ends.
    • Special Feature: Mostly found in urinary/vaginal infections.
  • Pollen Grains:
    • Appearance: Large, rounded, or oval with a well-defined, thick cell wall and/or regular/short projections.
    • Special Feature: Contamination from the urine or containers
  • Starch Granules:
    • Appearance: Colorless, birefringent, irregularly rounded; sometimes display a central slit/indentation; "Maltese crosses" with polarized light.
    • Special Feature: Exogenous contaminant often associated with baby powder.

Test your knowledge on histology and the characteristics of various types of epithelial and urinary casts. This quiz covers fundamental aspects of squamous and transitional epithelial cells, as well as different cast types in renal pathology. Perfect for students in medical or biological sciences seeking to reinforce their understanding of these concepts.