Urinalysis Crystals and Casts: Types, Causes, and Significance in Veterinary Medicine

Hyaline casts

Pure protein precipitates.

Hyaline casts appearance

Transparent, have parallel sides and rounded ends, and are composed of mucoprotein.

Hyaline casts occurrence

May occur with fever, exercise, and renal disease; may be seen in normal urine.

Epithelial cellular casts

Form from entrapment of sloughed tubular epithelial cells in the mucoprotein; may be seen with renal tubular disease.

Calcium oxalate crystals

Unusual form associated with ethylene glycol toxicity (antifreeze poisoning).

Calcium oxalate crystals appearance

Small, flat, colorless, and shaped like picket fence posts.

Ammonium acid urate crystals

Suggest liver disease (e.g., portosystemic shunt).

Ammonium acid urate crystals occurrence

Crystals occur in acidic urine and are yellow-brown spheres with irregular, spiny projections but may be amorphous.

Cystine crystals

Six-sided and variable in size; seen in acidic urine and represent proximal tubular defect in amino acid reabsorption.

Cystinuria

Has been reported in many dog breeds and rarely in cats, with high incidence in Dachshunds, Newfoundlands, English Bulldogs, and Scottish Terriers.

Calcium oxalate crystalluria

Occurs less commonly in dogs and cats; if persistent, may indicate an increased risk of calcium oxalate urolith formation.

Calcium oxalate dihydrate crystals

Appear as colorless squares with an X in the middle or envelope-shaped.

Calcium oxalate monohydrate crystals

Are dumbbell-shaped.

Granular casts

Thought to represent degenerated epithelial cellular casts.

Waxy casts

Have a granular appearance and arise from the degeneration of longstanding granular casts; typically have sharp borders with broken ends.

Struvite crystals

Commonly seen in canine and feline urine.

Struvite crystalluria in dogs

Is not a problem unless there is a concurrent bacterial urinary tract infection with a urease-producing microbe.

Struvite crystals without infection

In dogs, are not associated with struvite urolith formation.

Struvite uroliths in cats

May form without a bacterial urinary tract infection, which may be pathologic.

Struvite crystals appearance

Appear as colorless coffin lids or prisms but may be amorphous.