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Urinalysis Crystals

What are urine crystals?

Crystalluria- an oversaturation of crystal sediment in urine specimen

Many factors can contribute to their formation so some types are less clinically significant than others. It is important to identify & distinguish these crystals with a fresh, unrefrigerated urine specimen. 

  • *Note: Even if its considered significant or not, if there are massive amount of any type of crystal it can mean something clinically significant. So it is important to take note of it.

    • For example, even though ​uric acid crystals are common in urine it can be an indicator of gout if seen in large amounts.


Below is list of clinically significant & clinically insignificant (common) crystals:

  • Acid Crystals

  • Alkaline Crystals

Clinically Insignificant 

(Common Crystals)

  • Uric acid

  • Calcium Oxalate

  • Amorphous Urates

  • Triple Phosphate

  • Ammonium Biurate

  • Amorphous Phosphate

  • Calcium Carbonate

  • Calcium Phosphate

Clinically Significant

(Abnormal Crystals)

  • Amino Acid Crystals:

    • Leucine​

    • Tyrosine

    • Cystine

  • Cholesterol​

  • Bilirubin

  • Ampicillin

  • Sulfonamides

UA Chart.jpeg
Acidic Urine Crystals
Amorphous Urates
Amorphorus Urates.jpg


  • Very small & yellow- brown granules in clusters

    • Similar to sand

  • "Brick Dust"- pink-orangish color​

    • caused by Uroerythrin deposits on urate crytals​

Crystal Makeup:

  • Sodium (Na+)

  • Potassium (K+)

  • Magnesium (Mg+)

  • Calcium (Ca+)

Clinical Indication:

  • Precipitation is enhanced by refrigeration

    • Indicates Old sample

    • Dissolves in when heated or in alkaline urine

    • Precipitates in acetic acid

Uric Acid
Uric acid crystal polarized light 2.jpg


  • Usually yellow to orange-brown

  • Birefringent under polarizing light

  • Diamond shape: 

    • may cluster as a "rosette"

Crystal Makeup:

Catabolism products of:​

  • Purine Nucleic Acid

Clinical Indication:

  • Gout (in large amounts)- inflammation in big toe

  • Cytotoxic drugs

Calcium Oxalate
Calcium oxalate.png


  • Colorless

  • Dihydrate form:

    • "Envelope" (Octahedral)

  • Monohydrate form:

    • "Dumbbell" or small ovoid​

  • Birefringent under polarizing light​

Clinical Indication:

  • Often seen in normal urine

  • High Ascorbic Acid

  • Ingestion of:

    • Tomatoes​

    • Asparagus

    • Spinach

    • Oranges

  • Ethylene Glycol Poisoning

Bilirubin Crystal.png


  • Fine needles

  • Can also be seen as granules or plates

  • Always yellow-brown

Clinical Indication:

  • Always considered abnormal

    • if very high concentrations of bilirubin in the urine

  • Liver disease

Confirmatory Test: Bilirubin Strip

Amino Acid Crystal: Tyrosine


  • Fine, delicate needles frequently seen in clusters of sheaves:

    • "Stacks of Wheat"

  • Colorless or yellow​


Clinical Indication:

  • Sometimes seen in severe liver disease

Seen more often than Leucine crystals because it is less soluble in acidic urine

Amino Acid Crystal: 


  • Yellow-brown Spheres with concentric/radial striations

  • Highly refractile

  • Can be seen in urine containing tyrosine crystals if alcohol is used to precipitate


Clinical Indication:

  • Sometimes seen in severe liver disease

Can be mistaken for fat globules (or vice versa)

  • Unlike fat globules, leucine will not stain with fat stains or appear as maltese cross under polarization

Bactrim (sulfonamide) has a similar appearance, so it is important to check patient history 

Amino Acid Crystal: Cysteine


  • Colorless, flat, hexagonal plates

    • Sides may be uneven​

    • Refractile

  • Crystals appear layered​ as it tends to clump​​

cysteine crystal.jpg

Clinical Indication:

  • Congenital cytinosis

  • Cystinuria & Homocystinuria

    • Deposits in tubules as caliculi/ kidney stones causing damage​

Can be confused with uric acid crystals

  • Use Sodium Cyanide Confirmatory Test to distinguish



  • Appear as long, thin, colorless needles or prisms

  • May aggregate in small clusters

  • If refrigerated, may form large clusters


  • Rarely seen

    • Large ampicillin dosage​



  • Clear, flat, rectangular plates with "notched corners"

  • Soluble in chloroform & ether

Clinical Indication:

  • Rarely seen

  • Always seen with positive protein & fat droplets, fatty casts or oval fat bodies

  • Seen in Nephrotic Syndrome & other renal damage

    • Conditions that produce chyluria​



  • Highly refractife & birefringent

  • Yellow-brown sheaves or clusters of needles

sulfonamides crystals.png

Clinical Indication:

  • Seen in patients undergoing antimicrobial therapy with sulfa-drugs

    • Sulfa-drugs have now been modified to be more soluble, so sulfonamide crystals are actually rarely seen



  • Yellow to brown bundles of wheat

    • Constriction may be central or excentric​



Bactrin & Septim more commonly seen

  • Brown rosettes or spheres with irregular striations

Alkaline Urine Crystals
Amorphous Phosphates
Amorphous Phosphate crystal.png


  • Fine, colorless masses resembling sand

Clinical Indication:

  • Normal in urine- Clinically Insignificant

    • tends to obscure other more significant sediment​

    • Presence is enhanced by refrigeration

Microscopically indistinguishable from amorphous urates:

  • Distinguishable by urine pH & solubility

  • Amorphous phosphate will precipitate white rather than the pink- orange of amorphous urates

  • Soluble in acid & will not dissolve when heated to 60°C

Triple Phosphate
Triple Phoshate crystal.jpg


Colorless and will comes in different forms & sizes:

  • Coffin Lids- most common form

  • may also be seen as fern leaf or feather​​


  • Can be seen in normal healthy individuals

  • Associated with UTI

    • Present in formation of caliculi

Triple Phoshate.jpg

Also called Struvite

Calcium Phosphates
Calcium Phosphate Crystal.png


  • Colorless thin prisms in rosettes or star-shaped

    • "Stellar Phosphates"​

      • Tend to have 1 tapered or pointed end & the other end is squared off​

Calcium phosphate.jpg
Ammonium Biurate
ammonium biurate.png
Thorny Apple.jpg


  • Yellow-brown spheres with striations

  • Can have irregular spicules & spines

    • "Thorny Apple"

Clinical Indication:

  • Usually seen in old specimens

  • Not clinically significant unless seen in fresh urine

Calcium Carbonate
Calcium Carbonate crystals.jpg


  • Very small granular crystals

  • Can be misidentified as bacteria

  • Usually found in pairs

    • "Dumbbell Shape"​ or spheres


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