Granular casts in urine: an early warning of nephrotoxicity
10-year-old crossbreed dog receiving intravenous gentamicin for 5 days for a multidrug-resistant infection. A follow-up urinalysis is performed.
| Parameter | Result | Reference |
|---|---|---|
| Granular casts | 6–8/low-power field | 0–occasional hyaline |
| Urine glucose | + | Negative |
| Urine specific gravity | 1.014 | > 1.030 |
| Creatinine | 1.2 mg/dL | 0.5–1.5 |
Which interpretation and action are correct?
chevron_right Show answer and explanation
A. Normal finding with no clinical significance
Only the occasional hyaline cast is normal. Several granular casts per field indicate active tubular injury.
B. Tubular injury from the aminoglycoside: stop gentamicin even though creatinine is normal
Correct. Granular casts derive from degenerating tubular cells and, together with glucosuria and loss of concentrating ability, appear before azotaemia. The nephrotoxin must be withdrawn and renal function monitored.
C. They indicate pyelonephritis: add a second antibiotic
Pyelonephritis is associated with white cell casts, pyuria and bacteriuria, not with granular casts in this context.
D. Continue treatment and repeat creatinine; stop only if azotaemia appears
By the time creatinine rises, much of the function has already been lost. The sediment allows nephrotoxicity to be detected earlier and prevented.
lightbulb Key takeaway
If you use aminoglycosides, perform a urinalysis every 1–2 days: casts, normoglycaemic glucosuria or a fall in specific gravity are reasons to stop. Once-daily dosing, good hydration and avoiding other nephrotoxins (NSAIDs, furosemide) reduce the risk.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.