Urine sediment
Urine ·Also called: sediment, microscopic exam, urine microscopy, casts, crystals
What it is
Spinning urine collects the solid material at the bottom of the tube. That deposit is examined for red and white blood cells, bacteria, epithelial cells, crystals, and casts — the microscopic moulds of kidney tubules that only form inside the kidney itself.
Why your vet measures it
Almost every abnormal dipstick result needs the sediment to be interpreted. Protein with white cells and bacteria is infection; protein with a clean sediment points at the kidney filter. Casts are the one finding that localises a problem to the kidney itself rather than anywhere downstream.
What a positive result can mean
- White blood cells and bacteria — a urinary tract infection
- Red blood cells — bleeding from stones, inflammation, a tumour, or the collection method
- Struvite crystals, associated with alkaline urine and, in dogs, with infection
- Calcium oxalate crystals, associated with acidic urine and with high blood calcium
- Casts, which point to active kidney tubule damage
- Epithelial cells, usually from the bladder or urethral lining, occasionally from a tumour
What a negative result means
- A quiet sediment with only occasional cells is the normal finding
Dogs and cats differ
Crystals can form in the tube after collection, especially if the sample has been refrigerated, so crystals alone do not mean your pet is forming stones. This artefact is common in both species and is why a fresh, promptly examined sample is worth the effort.
Questions worth asking your vet
- How long after collection was the sediment examined?
- Do the crystals found match a stone type we should be preventing?
- Were any casts seen, and what does that mean for the kidneys?
Related terms
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