Urine Crystal Notes

Microscopic Examination of Urine Crystals

Crystal Formation

  • Crystals are formed by the precipitation of urine salts, organic compounds, and medications.

  • Factors influencing crystal formation:

    • Temperature

    • pH (very important in determining crystal type)

    • Urine concentration

  • Crystals can be found in healthy individuals and many types are relatively harmless.

  • -              Urine sediments that have specific shapes under microscopy

    -              Crystals result from the precipitation of urine solutes out of solution

    o   Formed by the precipitation of urine salts, organic compounds, and medication

    o   Form as urine cools to room or refrigerator temperature (depending on storage) – not clinically significant

    -              If crystals are formed in fresh urine, they were formed in vivo (in the body) and are clinically significant

    -              If crystals form within the nephrons, they can cause significant tubular damage

    -              Crystals are identified based on their microscopic appearance and the pH at which they are present

    o   pH – very important in determining type of crystal formation

    §  Some form an acidic pH and some at a basic pH

Formation Process

  • Ultrafiltrate passes through renal tubules.

  • Solutes become concentrated.

  • Increased solute concentration leads to saturation of the ultrafiltrate.

  • Crystals then precipitate.

Normal Crystals in Urine

  • Triple Phosphate

  • Calcium oxalate

  • Uric Acid

  • Hippuric Acid

  • Ammonium biurate

  • Calcium phosphate

  • Calcium carbonate

  • Amorphous

Abnormal Crystals in Urine

  • Bilirubin

  • Cholesterol

  • Leucine

  • Cysteine

Uric Acid Crystals

  • pH: Acidic

  • Solubility: Soluble in alkali and heat.

  • Color: Yellow to orange/brown or colorless.

  • Shape: Pleomorphic shapes include four-sided plates, rhombic plates, wedges, and rosettes.

  • Polarization: Appear multicolored under polarized light.

  • Clinical significance: Associated with gout, treatment with chemotherapy, and Lesch-Nyhan syndrome.

Calcium Oxalate Crystals

  • pH: Acidic, neutral, or alkaline

  • Dihydrate form:

    • Shape: Colorless octahedrons described as “envelopes.”

    • Polarization: Do not polarize light.

    • Association: Predominate in urine from patients with diets rich in oxalic acid and are the most common cause of kidney stones.

  • Monohydrate form:

    • Shape: Described as dumbbells or rings.

    • Association: Predominate in urine from patients who have ingested ethylene glycol (antifreeze).

Hippuric Acid

  • Color: Yellow-brown or colorless

  • Shape: Elongated prisms or plates, may be thin and resemble needles; often cluster together.

  • pH: Acidic or neutral

  • Solubility: Soluble in ether

  • Clinical significance: Little to no clinical significance, but may be associated with ethylene glycol intoxication.

Calcium Phosphate

  • pH: Neutral to alkaline

  • Shape: Colorless, blunt-ended needles, prisms, or rosettes

  • Association: May be associated with renal calculi

Triple Phosphate

  • pH: Alkaline

  • Shape: Colorless prisms described as “coffin lids.”

  • Polarization: Demonstrate birefringence under polarized light.

  • Clinical significance: Presence in urine is considered clinically insignificant; commonly seen in dog urine samples.

Calcium Carbonate

  • pH: Alkaline

  • Color: Small, yellow to colorless

  • Shape: Granules, dumbbell or spherical shapes with radial striations

  • Clinical significance: Not clinically significant but can be confused with other elements.

  • Unique feature: Crystals effervesce with hydrochloric acid or acetic acid, helping to confirm their presence.

Ammonium Biurate (Urate)

  • pH: Alkaline

  • Color: Yellow-brown

  • Shape: Spicule-covered spheres described as “thorny-apples.”

  • Clinical significance: May be clinically significant if formed in-vivo (dehydration).

Amorphous Crystals

  • Amorphous urates:

    • pH: Acidic

    • Color: Yellow to brown granules

    • Appearance: Appear as pink sediment (uroerythrin) in refrigerated samples.

    • Solubility: Dissolve at alkaline pH or heating above 60^\circ C

  • Amorphous phosphates:

    • pH: Alkaline

    • Appearance: Identical appearance to urates but colorless; white sediment in refrigerated samples.

    • Solubility: Soluble in acetic acid; do not dissolve when heated above 60^\circ C

Bilirubin

  • pH: Acidic

  • Shape: Needle-like to granular

  • Color: Yellow to brown

  • Associated with hepatic disorders/severe liver disease

Cholesterol

  • pH: Acidic

  • Shape: Colorless, rectangular plates with notched corners

  • Solubility: Soluble in chloroform and ether; insoluble in dilute acids and alkalis

  • Associated with nephrotic Syndrome and other disorders that produce lipiduria

  • Distinction: Differentiate from radiographic contrast media based on specific gravity

Cystine

  • pH: Acidic

  • Shape: Colorless thin hexagonal plates

  • Solubility: Soluble in HCL, sodium hydroxide, ammonium hydroxide; insoluble in acetic acid

  • Associations: Associated with inborn errors of metabolism such as hereditary cystinosis or cystinuria; most common cause of kidney stones in children

  • Confirmation: Confirmed by cyanide-nitroprusside test (turns red-purple)

Leucine

  • pH: Acidic

  • Shape: Yellow-brown spheres with concentric circles

  • Birefringent under polarized microscopy

  • Presence is associated with inborn errors of metabolism

Tyrosine

  • pH: Acidic

  • Shape: Colorless to yellow-brown single needles, sheaves, or rosettes

  • Associated with inborn errors of metabolism such as tyrosinemia and certain liver disorders in which amino acid metabolism is impaired

Crystals from Medication

  • Ampicillin

    • pH: Acidic

    • Shape: Colorless needles that may form in bundles

  • Sulfonamide

    • Color: Colorless to yellow-brown

    • Shape: Needles, sheaves of wheat, fan formations or rosettes

    • pH: Acidic

    • Solubility: Soluble in acetone and alkali; insoluble in acetic acid

  • Indinavir

Radiopaque Dye Crystals

  • Appearance: Flat needles or sheaves accompanied by round globules; variable in form

  • Confirmation: Consult ordering location to confirm administration of contrast media if suspected

  • Association: Associated with very high specific gravity results by refractometer (>1.035); reagent test pad specific gravity not affected by these crystals