Urolithiasis

Urolithiasis is the medical term for stones forming somewhere along the urinary tract, most often in the bladder but sometimes in the kidney, the ureter (the tube linking kidney to bladder), or the urethra (the tube that carries urine out). The stones themselves are called uroliths, and they form when minerals normally dissolved in urine clump together into solid pieces. Sizes range from gritty sand-like fragments to stones several centimetres across, and a pet can have one or dozens at once.

Stones are not the same as crystals. Microscopic crystals in a urine sample (crystalluria) are common and usually harmless on their own, particularly in cats. Stones are the larger, visible problem, and they cause trouble by irritating the bladder wall or physically blocking urine flow, which is what turns this from an uncomfortable condition into an emergency.

The two stone types seen most often in dogs and cats are struvite (made of magnesium, ammonium and phosphate) and calcium oxalate, and together they account for the vast majority of cases in both species. The distinction matters for treatment: struvite stones can usually be dissolved with a therapeutic diet, often over a few weeks to a couple of months, while calcium oxalate stones cannot be dissolved at all and have to be physically removed if they're causing problems. In dogs, struvite stones are typically linked to a urinary tract infection with bacteria that alter the urine's chemistry, so treatment usually combines diet with antibiotics, whereas in cats struvite more often forms without any infection at all. Less common types, including urate and cystine, have strong breed links, most notably urate stones in Dalmatians, where a hereditary quirk in how the body handles uric acid drives stone formation. Because you can't reliably tell stone type by looks alone, vets send retrieved stones for lab analysis, which is what makes accurate long-term prevention possible.

Signs and when it becomes urgent

Stones tend to look like a stubborn urinary tract infection. Watch for:

• Frequent trips to urinate, often producing only a few drops
• Straining, or crying out while trying to go
• Blood in the urine, or urine that looks pink or brown
• Accidents in the house, or a cat urinating outside the litter tray
• Low energy or going off food, especially alongside belly pain

A pet who is straining repeatedly and passing nothing needs to be seen immediately, not tomorrow. A complete blockage stops waste and potassium from clearing out of the blood, and complete obstruction can cause a life-threatening buildup of toxins within one to two days. This is far more common in male cats, whose urethra is narrower, and it's treated as one of the true emergencies in small animal practice. Cats treated promptly have a good chance of survival, though blockages can recur in a meaningful share of cases afterwards.

Treatment depends on the stone type, its location, and its size. Consensus guidance from veterinary internal medicine specialists favours dissolving struvite stones with diet and treating any underlying infection, and using the least invasive option available for other stones, such as flushing small ones out or retrieving them with a scope, rather than defaulting straight to open surgery. Stones causing no signs and too large to enter the urethra may simply be monitored over time. Afterwards, prevention centres on keeping urine dilute, since increasing fluid intake reduces the risk of stones forming and recurring, usually alongside a high-moisture or prescription urinary diet and periodic urine checks or imaging, because recurrence is common with several stone types. Your vet is best placed to say which plan fits your pet's specific stone type.