Microscopic UA Part 3 - Crystals

Urinary Crystals Formation

• Formed by precipitation of solutes (salts, meds, metabolites)

• Influenced by:

  • Temperature: lower temps → ↑ precipitation

  • Solute concentration: ↑ [conc] → ↓ solubility

  • pH: affects both crystal formation and ID

Abnormal Urinary Crystals

May indicate:

• Liver disease

• Inborn errors of metabolism

• Renal disease

• Renal calculi (kidney stones)

Crystal Identification in Urinalysis

• Morphology: Shape, color, size

• pH: Determines crystal type

• Polarized light: ability to polarize light

• Solubility testing:

  • Insoluble = remains crystalline

  • Soluble = dissolves with pH or temperature

    • Example: Amorphous urates dissolve in alkaline (NaOH) or heat (Soluble)

"Normal" Crystals in Urine

• onsidered normal when their concentration is low and the patient is healthy

• "Normal" is a relative term—context matters

Amorphous Crystals Overview

• Non-crystalline: no defined shape (don't confuse with granular casts)

• Amorphous. = No morphology

• No clinical significance

• Form in acidic or alkaline urine, depending on type

Amorphous Urates (Acidic Urine)

• Common in refrigerated samples

• Made of Ca²⁺, Mg²⁺, Na⁺, K⁺ urates

• Pink sediment; brown-pink granules microscopically

• Soluble in heat and alkaline conditions

Amorphous Phosphates (Alkaline Urine)

• Composed of phosphates and calcium

• Sediment is white

• Soluble in acetic acid

• Much more rare

• Not clinically significant

Sodium Urate Crystals

• Normal finding, often seen after refrigeration

• Caused by protein-rich diet

• Not clinically significant; typically not reported if observed in specimens

Uric Acid Crystals

• Found in acidic urine

• Normal in low concentrations

• Increased levels associated with:

  • Gout

  • Acute febrile conditions

  • Chronic nephritis

  • Lesch-Nyhan syndrome (excess uric acid)

• Soluble in alkali and heat

  

Uric Acid Crystal Morphology

• Color: Typically yellow or brown; may also be colorless

• Forms: Highly variable

  • Barrels

  • Rhombic plates

  • Rosettes

• Morphology helps in identification but varies widely in shape

Uric Acid Crystal: Polarized Light Properties

• Highly birefringent under polarized light

• Exhibits colorful, refractive patterns

• Helps differentiate from cystine crystals, which do not show birefringence

Calcium Oxalate Crystals

• Found in acidic to slightly alkaline pH

• Soluble in HCl

• Insoluble in acetic acid

• Morphologies: dumbbell, rectangular, octahedral ("envelope"), ovoid

• Frequently encountered; common in kidney stones

Calcium Oxalate Basics

• Common in acidic urine, but also seen in neutral to slightly alkaline pH

• Soluble: hydrochloric acid (HCl)

• Insoluble: acetic acid

• Major component of kidney stones

Calcium Oxalate Forms

• Dihydrate: envelope-shaped (two pyramids base-to-base), most common

• Monohydrate: dumbbell, oval, or rectangular (can resemble RBCs)

• Long monohydrate form linked to ethylene glycol poisoning

Calcium Oxalate Crystal Morphology

• Possible shapes: dumbbell, rectangular, octahedral (envelope), ovoid

• May require polarized light to differentiate from RBCs

• Calcium oxalate crystals polarize light

Clinical Relevance of Calcium Oxalate

• Associated with:

  • Renal calculi (kidney stones)

  • Oxalic acid poisoning

  • Liver disease

  • Ethylene glycol poisoning (especially long monohydrate form)

• May be confused with hippuric acid crystals—note shape differences

Hippuric Acid Crystals

• Rare, colorless prisms/needles/plates in acid, neutral, or alkaline urine

• Soluble in alkali, hot water

• Associated with benzoic acid–rich diets, liver dysfunction, and toluene exposure

• May resemble Ca oxalate monohydrate or triple phosphate—differentiate by solubility and weak polarization

Ammonium Biurate Crystals

• Appearance: “Thorny apples,” yellow-brown, seen in alkaline urine

• Soluble in: Acetic acid, heat

• Significance:

  • Only relevant in freshly voided urine

  • Typically an artifact from old/improperly stored specimens

• Note: Converts to uric acid crystals with acetic acid addition

Calcium Carbonate Crystals

• Found in alkaline urine

• Morphology: Dumbbell or spherical shape; may resemble granules

• Solubility: Effervesces with HCl and acetic acid

• Differential ID: May be confused with yeast or RBCs—confirm with solubility and morphology

→ Watch for misidentification due to small, round appearance in clumps or singly

Calcium Phosphate Crystals

• Appearance: Colorless; large flat plates, rosettes, or wedge-shaped prisms

• Urine pH: Alkaline

• Solubility: Dissolves in dilute acetic acid

• Notes:

  • Rosette form may mimic sulfonamide crystals (distinguished by solubility: sulfonamides do not dissolve in acid)

  • Can appear in normal urine

  • May be associated with kidney stones

Triple Phosphate (Ammonium Magnesium Phosphate)

• Appearance: Colorless, prism-shaped ("coffin lid"); may appear feathery as they dissolve

• pH: Alkaline urine

• Solubility: Soluble in acetic acid

• Polarized Light: Birefringent

• Formation: Common in alkaline urine due to bacteria that split urea into ammonia & CO₂

Contextual Note:
Often seen in urinary tract infections; appearance can vary—classic coffin-lid crystals may shift to feather-like shapes as they dissolve.

Abnormal Crystals – Key Features

• pH: Typically found in acidic urine

• Significance: Clinically significant; may indicate underlying pathology

• Confirmation: Identification may require chemical testing, patient history, or input from a specialist/pathologist

Cystine Crystals

• Appearance: Colorless, thin, hexagonal plates

• Found in: Acidic urine

• Solubility: Soluble in HCl, NaOH, NH₄OH

• Polarized light: No birefringence (differentiates from uric acid)

• Associated condition: Cystinuria — an inherited metabolic disorder causing defective reabsorption of cystine by renal tubules

• Clinical relevance: Most frequent cause of kidney stones in children

• Differentiation tip: May resemble uric acid crystals; distinguish based on lack of birefringence and solubility profile

Cholesterol Crystals

• Appearance: Clear, flat, rectangular plates with a notched corner

• Urine type: Acidic

• Solubility: Soluble in chloroform, ether

• Polarized light: Birefringent (brightly colored under polarization)

• Associated conditions:

  • Nephritis, nephrotic syndrome (excess tissue breakdown)

  • Chyluria (obstructed lymph drainage from tumors, filariasis, lymph node enlargement)

• Additional notes:

  • Rare in urine; lipids typically remain as droplets

  • Refrigeration may artifactually cause appearance

Tyrosine Crystals

• Appearance: Very rare; colorless to yellow-brown. Fine, sharp needles—may appear singly, in sheaves, or rosettes.

• Solubility: Soluble in HCl and NH₄OH

• Urine pH: Acidic

• Bilirubin test: Positive

• Seen in:

  • Severe liver disease

  • Inherited amino acid metabolism disorders (e.g., tyrosinemia)

  • Often appears with leucine crystals

Contextual clue: Presence suggests hepatic dysfunction—especially if both tyrosine and leucine are observed.

Leucine Crystals

• Morphology: Yellow-brown spheroids with concentric rings (outer edge) and radial striations (center)

• Found in: Acidic urine

• Soluble in: NaOH, hot water

• Associated Conditions:

  • Severe liver disorders (e.g. cirrhosis, severe viral hepatitis)

  • Maple syrup urine disease

  • Amino acid metabolism disorders

• Often seen with: Tyrosine crystals

• Bilirubin test: Positive

• Pitfall: May be confused with sulfonamide crystals (distinguishable by structure). Many antibiotics have sulfonamides in them. Perform solubility test to distinguish between the two.

Bilirubin Crystals

• Appearance: Yellow-brown (sometimes bright orange) needles or granules, often in clumps or attached to cells

• Urine pH: Acidic

• Solubility: Acetic acid, HCl, NaOH, acetone

• Bilirubin test: Positive, won’t see this otherwise

• Clinical context: Seen in severe liver disorders; correlate with patient history and jaundice

• Additional notes: Can be mistaken for amorphous material; distinct spiky needle bundles

Radiographic Dye Crystals

• Appearance: Flat needles or sheaves; highly variable

• May mimic: Cholesterol, tyrosine, sulfonamides

• Polarized light: Strong birefringence

• Key ID clues:

  • Recent radiographic procedure (history essential)

  • Very high specific gravity (>1.035)

Sulfonamide Crystals – Morphology & Clinical Context

• Appearance: Brown crystals seen as spheroids, flat needles, or sheaves of small needles

• Urine pH: Acid

• Solubility: Acetone & alkali

• Cause: Seen in patients taking sulfonamide antibiotics

• Associated: Risk of kidney stone formation, especially with dehydration

• Clinical tip: Confirm via medical history

Sulfonamide Crystals – Differential Diagnosis

• Can be mistaken for:

  • Leucine (spheroid, yellow concentric rings)

  • Tyrosine (fine needle sheaves/rosettes)

  • Radiographic dye (flat needles, high SG, birefringent)

• Clue: Sulfa crystals typically brown; patient history + hydration status helps confirm diagnosis.

Acyclovir Crystals

• Source: Anti-viral medication (e.g., herpes treatment)

• Urine pH: Neutral to slightly alkaline

• Morphology: Long, thin, needle-like crystals

• May be confused with: Tyrosine crystals

• Clinical tip: Confirm with patient medication history

Ampicillin Crystals

• Cause: High-dose ampicillin + poor hydration

• Morphology: Colorless needles; may clump post-refrigeration

• Key ID Clue: Appear bundled after refrigeration

• Diagnostic Tip: Confirm via medication history

Artifacts (Contaminants in Urine)

• Cause: Poor collection technique or dirty containers

• Common Populations: Pediatric or nursing home patients

• Lab Handling: Usually not reported unless contamination impedes analysis

Talcum Powder (Artifact)

• Appears as flat sheets

• May be confused with cholesterol or other crystals

Starch (Artifact)

• Highly refractile spheres with dimpled center

• May be confused with RBCs

• Shows a Maltese cross under polarized light

Oil Droplets / Air Bubbles (Artifact)

• Highly refractile, spherical objects

• May mimic RBCs under light microscopy

• Oil tends to float; air bubbles may have a dark edge or central refractile ring

Pollen Grains (Artifact)

• Large, spherical with distinct cell wall

• Often contain concentric circles

• Morphology may vary (can appear spiked or lobulated)

• May be mistaken for parasitic ova or other large cells

Hair and Cloth Fibers (Artifact)

• May mimic casts or parasites

• Types: clothing, diaper, cotton fibers

• Key distinguishing traits:
  • Highly refractile
  • Lack cast outline

• Careful observation under light microscopy essential

Fecal Contamination (Artifact)

• Source:
  • Improper collection (especially in infants)
  • Entero-urinary fistulas

• Microscopy:
  • Irregular debris resembling plant material, meat fibers, or other gut contents

• Interpretation tip:
  • Consider patient age and clinical history

Schistosoma haematobium (Parasite)

• Type: Trematode (fluke)

• Habitat: Bladder venous plexus

• Egg morphology: Oval with terminal spine

• Clinical relevance:
  • Associated with hematuria, bladder inflammation
  • Risk factor for squamous cell carcinoma of the bladder

• Diagnosis: Microscopic ID of eggs in urine (not stool)

Trichomonas vaginalis

• Most common urinary parasite

• Pear-shaped flagellate with undulating membrane

• Motile in fresh specimens

• Non-motile forms mimic WBCs or epithelial cells

• Confirm via patient history or video microscopy

Enterobius vermicularis (Pinworm)

• Intestinal nematode

• Eggs or worms enter urine via fecal contamination

• Most common in children

• Oval, flattened eggs with a thick shell

Contextual Note: Not a true urinary parasite—presence indicates contamination or fistula.

Giardia lamblia

• Intestinal protozoan

• Pear-shaped with flagella and two nuclei ("face")

• Rare in urine; enters via fecal contamination

• Often mistaken for debris or epithelial cells

Mites (Urine Contaminants)

• Type: External skin parasites (e.g., Sarcoptes scabiei, dust mites)

• Entry into Urine: Contamination

• Note: Dust mites often environmental; scabies mites may indicate true infestation