Urine Sediment & Crystal Reference for Dogs and Cats
Reference for the crystals and casts you'll see on urine sediment exam - appearance and clinical significance for each, in dogs and cats.
Crystal and cast findings should always be read in clinical context.
Sample handling matters - crystals can form in vitro as urine cools or sits, so correlate with a fresh sample, urine pH, and the patient's clinical picture rather than the crystal alone.
Sediment type
Crystal
Struvite (magnesium ammonium phosphate)
Appearance
Classic "coffin lid" rectangular prism shape.
Common and often incidental in normal alkaline dog urine in small numbers; larger numbers, especially with concurrent urinary tract infection, are associated with urease-producing bacteria (Staphylococcus, Proteus) that alkalinize urine and promote struvite urolith formation, and with idiopathic feline lower urinary tract disease (FLUTD) in cats.
Frequently asked questions
Are struvite crystals always abnormal?
No - small numbers are common and often incidental in normal, especially alkaline, dog urine; concern rises with large numbers, concurrent infection, or urolith formation, and struvite crystals are handled somewhat differently in cats where they're linked to idiopathic FLUTD.
What crystal is classically linked to ethylene glycol toxicity?
Calcium oxalate monohydrate crystals, seen in large numbers alongside a compatible exposure history and clinical signs - though their presence alone isn't diagnostic without the full picture.
Why do Dalmatians commonly show ammonium biurate crystals even when healthy?
Dalmatians have a unique inherited defect in purine/uric acid metabolism that predisposes them to ammonium biurate crystalluria and urate stone formation, independent of liver disease - though the same crystal in other breeds should prompt investigation for a portosystemic shunt.
What's the difference in significance between hyaline and granular/cellular casts?
Hyaline casts are nonspecific and can occur with mild, transient changes, while granular and cellular casts indicate active tubular damage or inflammation and are more clinically significant.