CONDITION
Ureteroliths
Ureteroliths are stones that form within the ureters — the narrow tubes that carry urine from each kidney down to the bladder. These stones develop when minerals in the urine crystallise and aggregate, most commonly calcium oxalate, and they may lodge at any point along the ureter's length. When a stone obstructs the flow of urine from a kidney, that kidney cannot drain, and pressure builds. Many animals with ureteroliths show no outward signs until a stone causes partial or complete obstruction. At that point, an owner may notice reduced appetite, quietness, vomiting, or straining in the litter tray, though the picture varies. Some stones are discovered incidentally during imaging for another reason. The condition occurs in both dogs and cats, with calcium oxalate ureteroliths seen more often in certain breeds — including miniature schnauzers and Yorkshire terriers in dogs, and Burmese, Persian, and Ragdoll cats. This page explores the signals an owner may observe, the mechanisms that lead to stone formation and obstruction, the imaging and laboratory work used to locate and characterise ureteroliths, and the range of approaches available when a stone is confirmed — from monitoring and dietary influence through to surgical or minimally invasive removal.
Why this matters now
Ureteroliths tend to be identified in middle-aged to older animals, with many cats and dogs diagnosed around seven to nine years of age. Certain breeds carry higher documented risk: in cats, Burmese, Persian, Ragdoll, British Shorthair, and Tonkinese have elevated predisposition to calcium oxalate stone formation, whilst in dogs, miniature schnauzers, Yorkshire terriers, bichon frises, and Shih Tzus show similar patterns. The stones may form over months or years before they cause obstruction or are detected incidentally during imaging for another concern.
The course varies widely. Some stones remain silent, causing no disruption to urine flow and discovered only when imaging is performed for unrelated reasons. Others migrate into the narrow ureteral channel and obstruct it partially or completely, triggering signs that may appear suddenly or evolve over days. If obstruction persists, the affected kidney may become distended with backed-up urine—a state termed hydronephrosis—and function in that kidney can decline, sometimes irreversibly if pressure is sustained.
Signals & patterns
Early signals
Episodes of vomiting
Intermittent vomiting may occur without obvious gastrointestinal cause, often reflecting discomfort or early metabolic disturbance as urine flow becomes impeded. The vomiting can be sporadic and may be attributed initially to dietary indiscretion or mild gastritis.
Blood in the urine
Urine may appear pink-tinged, red, or contain visible clots, reflecting irritation or trauma as the stone moves within the ureter or kidney. This sign can be intermittent and might be noticed in the litter tray, on paving, or during a routine urine sample.
Reduced appetite or quietness
The animal may eat less enthusiastically, seem less interested in play, or spend more time resting than usual. These changes often reflect a generalised sense of being unwell rather than localised pain that an owner can pinpoint.
Straining or frequent posturing
Some animals adopt a urinating posture more often than normal, sometimes producing small amounts of urine or none at all. This pattern can resemble lower urinary tract disease and may be mistaken for cystitis or urethral blockage.
Later signals
Persistent lethargy or collapse
As kidney function becomes compromised and waste products accumulate in the bloodstream, the animal may become profoundly weak, unresponsive, or unwilling to move. This reflects worsening azotaemia and the systemic effects of uraemia.
Dehydration or reduced skin elasticity
The skin may lose its normal spring when gently lifted, the eyes may appear sunken, and the mucous membranes may feel dry or tacky. These signs develop when vomiting, reduced fluid intake, and impaired kidney function combine to deplete the body's fluid reserves.
Complete absence of urination
If both ureters become obstructed, or if the single functioning kidney is blocked, urine output ceases entirely. This represents a severe disruption requiring intervention to restore flow and prevent irreversible kidney injury.
Click to read about the biological mechanisms
How this is usually investigated
Investigation typically begins with a thorough history—including any recent changes in urination, appetite, or behaviour—and a physical examination to assess comfort, kidney size, and bladder fullness. Blood and urine tests help clarify kidney function and identify metabolic factors that may have contributed to stone formation. Imaging then localises the stone, defines the degree of obstruction, and guides decisions about whether intervention is needed and what form it might take.
Chemistry panel
SDMA
Urinalysis with sediment
Abdominal ultrasound
Computed tomography (CT)
Options & trade-offs
Management is shaped by the degree of obstruction, the speed at which kidney function is changing, and the animal's overall stability. Some stones remain stable and cause little harm, allowing a period of monitoring, while others demand intervention to preserve kidney function. The approach chosen often combines elements—dietary adjustment, medical management to support urine flow, and in some cases procedures to remove or bypass the stone—and what works well for one animal may be less suitable for another.
Medical management and monitoring
In animals with partial obstruction or stones that are not causing progressive kidney injury, management may involve close monitoring of kidney markers, hydration support through increased water intake or subcutaneous fluids, and medications that relax the smooth muscle of the ureter or reduce inflammation to encourage the stone to pass. Pain relief is often provided during this period, and serial imaging tracks whether the stone is moving or the kidney is worsening.
Trade-offs: This approach avoids the risks of anaesthesia and surgery, but it requires patience and regular reassessment; there is no certainty that a stone will pass, and if kidney function declines, intervention may become necessary after a period of waiting.
Ureteral stenting or subcutaneous ureteral bypass
These are minimally invasive techniques that create a new route for urine to bypass the obstructed section of ureter. A stent is a narrow tube placed inside the ureter to hold it open, while a subcutaneous bypass uses a small tube tunnelled under the skin to carry urine from the kidney directly to the bladder. Both allow urine flow to resume without removing the stone itself.
Trade-offs: These procedures restore kidney drainage more quickly than waiting for a stone to pass and avoid the need for open surgery, but they require specialist training and equipment, carry risks of tube blockage or infection over time, and may need revision or replacement in some animals.
Surgical ureterotomy or nephrectomy
Ureterotomy involves making an incision in the ureter to remove the stone directly, then closing the tube; this is technically demanding given the ureter's small diameter and thin wall. If the affected kidney has lost most of its function and the other kidney is healthy, removal of the damaged kidney (nephrectomy) may be considered to eliminate a source of infection or discomfort.
Trade-offs: Surgery allows definitive removal of the stone and, in the case of ureterotomy, preservation of the kidney if it retains viable tissue, but it carries anaesthetic risk, potential for urine leakage or stricture formation at the surgical site, and a recovery period during which close monitoring is needed.
Dietary modification to reduce recurrence
Once a stone has been addressed, adjusting the diet to promote dilute urine, reduce urinary calcium excretion, and limit oxalate intake can reduce the likelihood of new stones forming. This typically involves feeding a prescription diet formulated for urinary health and encouraging higher water consumption through wet food, water fountains, or flavoured broths.
Trade-offs: Dietary change does not dissolve calcium oxalate stones that have already formed and cannot guarantee that new stones will not appear, but it is a low-risk component of long-term management that many owners find straightforward to sustain.
Common misconceptions
"A ureteral stone will always cause sudden, severe signs that make the diagnosis obvious."
Many ureteroliths develop gradually and may cause only vague signs such as reduced appetite, intermittent vomiting, or subtle changes in behaviour, particularly if the obstruction is partial or affects only one kidney while the other compensates. Some stones are discovered incidentally on imaging performed for an unrelated reason, before any clinical signs have appeared.
"Once a stone has been removed or bypassed, the problem is solved and no further management is needed."
Animals that have formed one calcium oxalate stone remain at higher risk of forming others, as the underlying metabolic and dietary factors that led to the first stone often persist. Long-term dietary management, regular monitoring of urine and kidney function, and attention to hydration are often part of ongoing care to reduce recurrence risk.
Related conditions
Urinary Stones (Urolithiasis)
Urinary stones can form in the kidneys and then migrate into the ureters, becoming ureteroliths; the same metabolic factors that drive bladder stone formation—such as urine concentration, pH, and mineral supersaturation—also influence whether stones develop higher in the urinary tract.
Hydronephrosis
Hydronephrosis often develops when a ureteral stone partially or completely obstructs the flow of urine from the kidney, causing the kidney's collecting system to stretch and swell as pressure builds upstream from the blockage.
Acute Kidney Injury
Acute kidney injury can occur when a ureteral stone causes complete obstruction of urine outflow, particularly if both ureters are affected or if the animal has only one functioning kidney; prolonged obstruction interrupts the kidney's ability to filter waste and maintain fluid balance.
Pyelonephritis
Pyelonephritis may develop alongside or as a consequence of ureteral obstruction, since stagnant urine and impaired drainage create conditions in which bacteria can ascend from the bladder and establish infection within the kidney itself.
Urethral Obstruction
Urethral obstruction and ureteral obstruction share a common presenting sign—straining to urinate—but differ in location and consequence; owners sometimes observe similar difficulty in both, though urethral blockage prevents bladder emptying entirely, while ureteral stones may allow partial urination if the bladder itself remains unobstructed.
If a ureteral stone has been identified or suspected, understanding how kidney function is being monitored over time and what factors in diet or metabolism may have contributed can be useful context for decisions ahead. For animals with a history of stones, exploring patterns in water intake, urine concentration, and any related conditions affecting calcium balance may clarify what adjustments might reduce the chance of recurrence. The metabolic health pillar offers broader background on how the kidneys process minerals and maintain fluid balance, which connects to the longer arc of urinary health.