Common crystals

Crystal pH Information

Ammonium biurate

Usually neutral to acidic: pH ≤ 7

Brown, spherical to irregular crystals ("thorny" apple)

Common in Dalmations, English bulldogs

In other breeds of dogs or cats suggests liver dysfunction and portosystemic shunting

May occur with amorphous urates or sodium urate (needles or prisms)

Amorphous

Phosphates: pH ≥ 7

Urates: pH ≤ 7

Small, irregularly shaped crystals

Can be of different composition (urates, xanthine, phosphate) depending on pH.

Can be seen in healthy animals

Mimic bacterial cocci - perform a gram stain to differentiate

Bilirubin

Acidic: pH < 7

Small needle-like to granular yellow or yellow-brown crystals

Indicates bilirubinuria due to conjugated (direct) bilirubin

Bilirubinuria can be normal in dogs but is abnormal in other species.

Calcium carbonate

Usually alkaline: pH ≥ 7

Spherical to irregular (rhomboid, dumb-bell, ovoid) yellow to colorless crystals. Spherical forms have radial striations.

Normal in horses, guinea pigs

Not normally seen in dogs, cats or ruminants.

Calcium oxalate dihydrate Usually neutral to acidic: pH ≤ 7

Colorless octahedrons, "envelopes"

Can be seen in healthy animals or in

animals with calcium oxalate uroliths

But can be seen with hypercalciuria or hyperoxaluria (ex. ethylene glycol or oxalate rich plant ingestion)

Develop over time with storage of urineMagnesium ammonium

phosphate (struvite)

Usually neutral to alkaline: pH ≥ 7

Can be seen in healthy dogs, cats and ruminants.

Also common in bacterial-induced alkalinuria and with sterile struvite or mixed uroliths

Uncommon crystals

Crystal pH Information

Uric acid

Acidic: pH < 7

Yellow, red-brown or brown, rarely colorless hexagonal plates or needles (rare)

Variable: Rhomboid to diamond crystals, often with pointed ends, hexagonal flat crystals, rosettes, barrel shapes

Calcium oxalate monohydrate

Usually neutral or acidic: pH ≤ 7

Oval, spindle, dumb-bell and picket shaped forms

Oval, spindle or dumb-bell forms are infrequently seen in urine from healthy dogs and cats but can be seen in hypercalciuric conditions and ethylene glycol toxicity

Picket fence form (arrow) are commonly observed in ethylene glycol toxicity in dogs and cats, but can also be seen in animals with hypercalciuria due to other causes (e.g. lymphoma)

Calcium phosphate Usually Colorless

neutral or alkaline: pH ≥ 7

Blunt-ended needles or prisms, often in rosettes, can be amorphous

Cystine

Usually neutral to acidic: pH ≤ 7

Flat colorless hexagonal plates, which often aggregate

Indicative of cystinuria, a rare inborn error of amino acid metabolism affecting many breeds of dogs.

Drug-associated

Variable but usually acidic: pH < 7

Various forms (needles, radiating bundles, round with striations), yellow to colorless

Can be seen in animals on certain drugs: e.g. sulfonamides (mimic various forms of urates), ampicillin (slender needles to sheaves), contrast media, primidone

The image on the left is a sulfonamide crystal (often forms fan-shaped structures) from a dog that was treated with trimethoprim-sulfonamide and sulfasalazine for a chronic urinary tract infection

Tyrosine

Acidic: pH < 7

Fine colorless to brownish needles

Indicate severe liver disease or conditions causing aminoaciduria in humans, but very rare in animals

Unknown crystalsNeedles

Variable pH All the crystals shown on the left were seen in the urine from dogs. Their identity is uncertain

Variable shape

Not clearly identified as any of the known crystals

Needle-like bundles

Flat plates resembling cholesterol

Solubility assessed with hydrochloric acid, acetic acid and sodium hydroxide - solubility characteristics do not match those of known crystals

Significance dependent on clinical signs and history