Casts in urine sediment (hyaline, granular, waxy) in cats and dogs
Casts are tiny cylinders of protein that form inside the kidney tubules and are washed out into urine — a cast of the tubule, like jelly set in a mould. Because they form only in the kidney, they point to the kidney rather than the bladder. A few hyaline or granular casts can be found in healthy animals; many casts, or waxy ones, suggest injury to the tubules.
What it shows
Casts are made mainly of a mucoprotein (Tamm-Horsfall protein) produced by the cells of the kidney tubules. Cells inside the tubule can be trapped in the protein as it sets. Cellular, granular and waxy casts are thought to be successive stages of breakdown of trapped tubular cells. The lab counts casts and names their type:
- Total casts — all casts together; the form may list types separately.
- Hyaline — clear protein casts without cells, hard to see and easy to confuse with mucus strands.
- Granular — grainy casts, usually from degenerated cellular casts.
- Waxy — smooth, glassy casts with squared-off ends, the last stage of breakdown.
Higher than reference — what it may be a sign of
- Hyaline casts — 0–1 per low-power field can be found in concentrated urine of healthy animals. More may appear with proteinuria, from overflow of protein from blood or from disease of the kidney filter (glomeruli); fever, exercise and kidney disease are also listed. Not every animal with proteinuria has them.
- Granular casts — low numbers of fine granular casts occur without tubular injury; a few in an animal with normal kidney values and no proteinuria are not by themselves a sign of tubular injury and may be transient. Many granular or cellular casts point to widespread, usually acute, kidney disease.
- Cellular casts — most often from reduced blood flow to the kidney or toxic damage; in a severely dehydrated animal they can become prominent after fluids are restored, when urine flow flushes them out.
- Waxy casts — indicate tubular injury and are always considered significant; they can occur in acute kidney injury or chronic kidney disease, probably with low urine flow.
Casts show that tubular injury is present, but not how extensive it is or whether it will recover.
Lower than reference
None or few is expected, and the absence of casts does not rule out kidney disease. Casts are unstable: they dissolve over time, especially in dilute or alkaline urine, so an older sample may show fewer than were in the bladder. They are also shed intermittently, and a single sample may show none even in acute kidney disease. That is why urine is best examined within 30 minutes of collection.
Look at together with
- Creatinine, urea and SDMA — whether kidney function has changed; a few fine granular casts with normal values are read calmly.
- Urine protein and UPC — hyaline casts often go together with protein loss.
- Specific gravity and pH — dilute or alkaline urine dissolves casts.
- Renal epithelial cells — tubular cells in the sediment support the same conclusion as cellular casts.
Units and conversion
Casts are counted per low-power field of the microscope (/lpf, 10× objective), together with the type, for example “5–10/LPF, granular”. The total is the sum of all types. Words such as “none” or “few” are used too. There is nothing to convert.
Reference range
The reference range is on your lab’s form; it is usually “none to few” per low-power field — one reference laboratory gives 0–few/LPF. In healthy animals casts are few or none and are usually hyaline or granular; waxy and cellular casts are not expected. The sample’s age matters: a sample tested late can look better than the urine really was.
Cats and dogs
Cats normally carry small to moderate amounts of fat in the cells of the kidney tubules. Fat therefore sticks to hyaline casts more easily, which makes “fatty” casts harder to judge in cats: fat droplets on a hyaline cast do not by themselves make it a fatty cast.
The sources describe casts in dogs in the same way as in cats, without dog-specific limits. Casts of muscle pigment (myoglobin) have not been reported in animals, so muscle injury is told apart from red-cell breakdown by CK in blood and by looking for haemoglobin in plasma and urine (see blood in urine), not by casts.
Add a lab form — Pet Tracker Space recognises the lines, keeps the form’s units and draws each indicator over time with your lab’s reference band.
Sources
This page explains what a lab value means. It is not a diagnosis and not a substitute for your veterinarian — only they can interpret results for your pet.