Microscopic Examination of Urinary Casts

Cylindruria; Unique to the kidney.

They represent a biopsy of an individual renal tubule; They are among the most difficult and most important urinary sediment constituents to examine.

Distal convoluted tubule (DCT) and collecting duct; Uromodulin or Tamm-Horsfall protein (THP), produced by RTE cells.

Albumin and immunoglobulins.

Casts with a tail; Have the same significance as casts.

Urine-flow stasis, acidic urine, and the presence of sodium (Na⁺) and calcium (Ca²⁺).

Even and definite outline; Parallel sides; Two rounded ends; Uniform diameter.

Approximately 7–8 times the diameter of an RBC.

Along the coverslip edges using subdued light.

Hyaline cast; It is the beginning or prototype of all cast types.

Most frequently encountered but most difficult to discover; Colorless and translucent; Normal value: 0–2/LPF.

Physiologic: Strenuous exercise; Pathologic: Glomerulonephritis, pyelonephritis, CHF, and CKD

RBC cast; Indicates bleeding within the nephron.

Easily identified by their orange-red color; Associated with glomerulonephritis and strenuous exercise.

A cast containing hemoglobin from lysed RBCs; Homogeneous with an orange-red color.

They have the same clinical significance.

Inflammation or infection within the nephron; Associated with pyelonephritis and acute interstitial nephritis.

RTE cast; Use phase-contrast microscopy and supravital staining.

A clump of leukocytes; It is not a true cast and should NOT be reported as a cast.

Lower urinary tract infection (UTI).

Cells visible on the cast matrix are smaller, round, and oval; Indicates advanced tubular destruction and tubular damage.

Identified using Gram stain; Associated with pyelonephritis.

Derived from lysosomes of RTE cells during normal metabolism (nonpathologic); Cells disintegrate when the cast remains in the tubule before being flushed out.

Sandpaper appearance.

Glomerulonephritis, pyelonephritis, stress, and strenuous exercise.

Fat globules are not stained; Only the cast matrix is stained.

Triglycerides and neutral fats: Lipid stains; Cholesterol: Polarizing microscope showing Maltese cross formation.

Nephrotic syndrome, toxic tubular necrosis, diabetes mellitus, and crush injuries.

Final degenerative form of all types of casts; Brittle and highly refractile with jagged ends; Ground-glass appearance.

Urine-flow stasis and chronic renal failure.

Renal failure casts; Indicate destruction and widening of tubular walls.

Yes; Granular and waxy casts are the most common broad casts.

2–6 times wider; Associated with extreme urine stasis and renal failure.

Crystalluria is the excretion of crystals in urine; Crystals form through precipitation of urine solutes, including salts, organic compounds, and medications.

They are the most recognized but the most insignificant part of urine sediment.

Concentrated urine specimen with increased specific gravity (SG).

Urine pH, solute concentration, and temperature.

Rare, few, moderate, or many per HPF; Abnormal crystals may be averaged and reported per LPF and generally require confirmation before reporting to the physician.

Composed of calcium, magnesium, sodium, and potassium urates; Fluffy orange or pink sediment (brick dust) due to uroerythrin; Microscopically, yellow-brown granules.

Clumps of amorphous urates that resemble granular casts.

Acetic acid: Converts them into uric acid; Ammonium hydroxide: Converts them into ammonium biurate.

Increased in gout and chemotherapy; Soluble in heat and alkali.

Product of purine metabolism; Most pleomorphic urinary crystal.

Rhombic (diamond), four-sided flat plate (whetstone), lemon-shaped, wedges, barrels, rosettes, irregular plates, and laminated forms.

Hexagonal forms.

Present at pH less than 5.7; Above 5.7, uric acid is in its ionized form as urate.

Increased in Lesch-Nyhan syndrome, chemotherapy, and gout; Soluble in alkali.

Dihydrate (Weddellite) and monohydrate (Whewellite); Dihydrate is more common.

Dihydrate (Weddellite): Envelope, bipyramidal, and octahedral; Monohydrate (Whewellite): Oval and dumbbell-shaped.

Calcium oxalate.

Foods rich in oxalic acid, such as tomatoes and asparagus; Increased ascorbic acid.

Ascorbate is metabolized into oxalate, which combines with calcium to form calcium oxalate.

Ethylene glycol (antifreeze agent) and methoxyflurane poisoning (malignant hyperthermia).

Dilute hydrochloric acid (HCl).

Calcium and magnesium phosphates; Fine or lacy white precipitate macroscopically and granular appearance microscopically.

Amorphous phosphates.

Dilute acetic acid.

Alkaline counterpart of uric acid and amorphous urates.

Yellow-brown thorny apples; Commonly seen in old urine specimens.

Presence of urea-splitting bacteria, which produce ammonia from urea.

Turns into uric acid; Soluble in heated acetic acid.

Magnesium ammonium phosphate (struvite).

Colorless, prism-shaped or coffin-lid appearance; May have fern-leaf appearance; Feathery appearance when disintegrated.

Presence of urea-splitting bacteria producing ammonia; Soluble in dilute acetic acid.

Colorless, elongated rectangular or rhomboid plates; May have notched ends or corners; Edges may be irregular or eroded; Soluble in acetic acid.

Dibasic calcium phosphate (stellar phosphate) and monobasic calcium phosphate.

Colorless, flat plates or thin prisms arranged in rosette form; Rosettes may resemble sulfonamide crystals.

Irregular, granular-appearing sheets or plates; Less common than the dibasic form.

Hydroxyapatite (basic calcium phosphate) and brushite (calcium hydrogen phosphate).

Dilute acetic acid

Small, colorless, dumbbell-shaped, tetrads, or spherical-shaped.

Produces gas with effervescence; May be misidentified as bacteria.

Colorless, refractile hexagonal plates, often laminated; May be mistaken for hexagonal uric acid crystals; Increased in cystinuria and cystinosis.

Uric acid: yellow-brown, insoluble in dilute HCl, birefringent, negative cyanide-nitroprusside reaction; Cystine: colorless, soluble in dilute HCl, not birefringent, positive cyanide-nitroprusside reaction; Both are soluble in ammonia.

Rectangular plates with notches in one or more corners (staircase pattern); May resemble radiographic dye crystals; Associated with nephrotic syndrome and lipiduria; Soluble in chloroform.

Flat, four-sided plates with a notched corner; May also appear as long, thin prisms or rectangles; Check patient history and correlate with other UA results, such as SG >1.040 using a refractometer; Soluble in 10% NaOH.

Fine, colorless to yellow needles arranged in clumps or rosettes; Increased in liver disease; More commonly found than leucine; Soluble in alkali or heat.

Yellow-brown, oily-looking spheres with concentric circles and radial striations; May resemble fat globules; Precipitate with tyrosine after adding alcohol; Increased in liver disease; Soluble in hot alkali or alcohol.

Bright yellow clumped granules or needles (Strasinger); Reddish-brown needles clustered in clumps or spheres (Turgeon); Granules and plates may also occur (Brunzel); Increased in liver disease; Soluble in acetic acid, HCl, NaOH, acetone, and chloroform.

Fan-shaped needles, sheaves of wheat, rosettes, arrowheads, petals, round shapes, and whetstones; May be mistaken for calcium phosphate; Calcium phosphate dissolves in acetic acid, while sulfonamide gives positive lignin test and diazo reaction.

May deposit in nephrons and cause tubular damage; Currently modified so solubility is no longer a problem; Soluble in acetone.

Sulfamethoxazole: brown rosettes or spheres with irregular radial striations; Acetylsulfadiazine and sulfadiazine: yellow-brown sheaves of wheat with eccentric binding.

Colorless needles that tend to form bundles after refrigeration; Increased with massive doses of penicillin.

Spherical structures with a dimpled center; Produce a Maltese cross formation under a polarizing microscope.

Oval fat bodies; Fatty casts; Fat droplets; Starch granules.

Oil droplets and air bubbles may be mistaken for RBCs; Hair and fibers may be mistaken for casts.

Pollen grains: spheres with a cell wall and concentric circles; Other possible artifacts include fecal contamination, hair, and fibers.