Kidney stones in dogs – symptoms, monitoring and treatment

Overview

Kidney stones and ureteral stones are in different places

A ureter carries urine from a kidney to the bladder. A stone lodged in it can prevent kidney drainage. The urethra, by contrast, carries urine out of the bladder, so urethral obstruction affects a different urinary tract location. Stone location determines the associated signs and treatment options.

Only a small proportion of urinary stones are in the kidneys or ureters. Finding a kidney stone that causes no problems does not itself mean surgery is needed. An estimated 20–30% of upper urinary tract stones in dogs are struvite, which may be dissolvable. Calcium oxalate stones do not dissolve with medication or diet.

Treatment aims to preserve kidney function and avoid unnecessary kidney tissue damage.

Causes

Minerals precipitate into stones

Stones form when urine minerals precipitate under suitable conditions as crystals and grow into stones. Concentrated urine increases the concentration of substances that can crystallise. Urine acidity also affects the solubility of different minerals. Inherited characteristics, metabolic diseases and infections can influence stone formation.

In dogs, struvite stones are often associated with urinary tract infection caused by urease-producing bacteria. Increased urinary calcium excretion can predispose to calcium oxalate stones. Urate stones can involve an inherited uric acid metabolism disorder or a liver shunt. Cystine stones result from impaired amino acid reabsorption in the kidney tubules.

Why can a stone's location become dangerous?

When urine flow is obstructed, backed-up urine dilates the renal pelvis. The ureter can also dilate above the obstruction. Increasing pressure can cause functioning kidney tissue to atrophy. Prolonged pressure damage can turn the kidney into a poorly functioning, fluid-filled sac. A growing kidney stone can also compress kidney tissue without moving into the ureter.

Risk factors

Assessing stone susceptibility considers the stone type and underlying diseases. Calcium oxalate stones occur more frequently in breeds such as Miniature Schnauzers, Bichons Frises and Shih Tzus. They form particularly in middle-aged and older dogs. High blood calcium and hyperparathyroidism can contribute to this susceptibility.

Dalmatians can have inherited hyperuricosuria, or high urinary uric acid excretion, predisposing to urate stones. Cystine stones are found most often in younger entire males. Urinary tract infection is particularly relevant to struvite stones. If the other kidney is already diseased, ureteral obstruction can cause clear uraemic signs.

Typical symptoms

A kidney stone may be found without problems that would require removal. A stone that has moved into a ureter can involve:

• Abdominal pain or discomfort.
• Reduced appetite.
• Tiredness and quietness.
• Vomiting.
• Blood in urine.

Fever can also occur if there is a kidney infection. Infection can involve increased drinking and urination. Typical lower urinary tract signs may be absent with ureteral obstruction. Obstruction on both sides, or disease in the other kidney too, can also cause dehydration and a marked decline in general condition.

Kidney infection can also involve weight loss. Infection may cause toileting accidents indoors or straining during urination.

Complications and consequences

Obstruction, infection and kidney damage

Ureteral obstruction can cause permanent loss of kidney function. The other kidney can compensate sufficiently that blood waste concentrations have not yet risen. Normal creatinine therefore does not exclude one-sided ureteral obstruction.

Dangerously high blood potassium can develop even without a detected heart rhythm disturbance. Kidney infection can cause acute kidney injury. Bacteria can also spread into the bloodstream.

In one series of 44 dogs with ureteral obstruction, 59% had a positive urine culture. Pus-filled infection of the renal pelvis with associated sepsis was found in 30%. These figures concern selected obstruction patients, rather than all symptom-free kidney stones.

Reobstruction after stent treatment has been reported in 9% of dogs. Recurrence can involve concurrent ureteral narrowing. How much function an individual kidney can recover cannot be reliably predicted.

Kidney stones are among the factors predisposing to kidney infection.

Diagnosis at the vet

Location, urine flow and kidney function

Ultrasound and X-rays are common tests for locating stones. Not every stone appears on plain X-rays. Ultrasound assesses the kidneys, ureters and bladder. An enlarged, painful kidney may also be felt on palpation.

Dilation of the renal pelvis and ureter above an obstruction supports the diagnosis. Renal pelvic dilation below 5 mm needs careful interpretation unless there is also ureteral dilation above an obstruction. If ultrasound does not show an obstruction, X-rays can complement the examination. No visible stone does not exclude obstruction from another cause, such as scar narrowing.

Blood tests assess general condition and kidney function. Potassium is measured because an increase can be dangerous. Urine assessment includes pH, crystals and bacterial growth. Urine culture is particularly important in canine ureteral obstruction. Culture susceptibility testing helps select an appropriate antibiotic for infection.

Stone composition is estimated from urine results and X-ray appearance. A removed stone undergoes quantitative mineral analysis where possible. Treatable calcium metabolism disorders are also investigated with calcium oxalate stones.

Treatment

When is monitoring enough?

Your vet may monitor a kidney stone that causes no obstruction, recurrent infection, pain or kidney tissue compression. Monitoring includes urine tests and urinary tract imaging. A growing stone or one causing problems is reassessed for treatment.

Treating obstruction in hospital

Dehydration and dangerous electrolyte disturbances are treated before or alongside the procedure. Urine drainage from the kidney must be secured. A stent, or internal tube, can be placed in the dog's ureter to bypass the stone. For a canine stone obstruction, a stent placed by an experienced operator is the first-choice option.

A stable patient's response may be assessed over 24–72 hours under hospital monitoring. This does not mean waiting that long at home with a confirmed obstruction. Conservative treatment alone is not continued if urine output remains low, potassium rises or kidney values worsen. Progressive renal pelvic dilation is another reason to relieve the obstruction. Close monitoring may be planned for some carefully selected stable patients if renal pelvic dilation is no more than 3–5 mm. The decision depends on the whole situation and an experienced treating vet's assessment.

Confirmed kidney infection is treated with an antibiotic selected using culture results. Severe kidney infection may require hospital care and intravenous fluids. A stent also helps bacteria and inflammatory debris drain from the infected kidney.

Dissolution, fragmentation or removal

Dissolution of a kidney stone consistent with struvite may be attempted through diet and infection treatment. Dissolution requires the stone to be surrounded by suitable urine. A blocked ureter is bypassed with a stent before dissolution if needed. Calcium oxalate stones do not dissolve, so a problematic stone may be removed or fragmented. The possibility of dissolving urate and cystine stones is assessed individually.

Less invasive stone removal methods are preferred where possible to protect kidney function.

Extracorporeal shockwave lithotripsy is generally suitable for kidney stones up to 1.5 cm in dogs. A ureteral stent may also be needed with a stone larger than 1–1.5 cm. A large stone or one unsuitable for lithotripsy can be removed using an endoscopy-assisted method. Lithotripsy has required repeat treatment in 15–50% of dogs. These procedures need specialist expertise.

Procedure outcomes

Mortality below 2% has been reported for canine ureteral stenting. Mortality for shockwave lithotripsy has been reported as below 2%. These figures concern procedure series, rather than an individual dog's outlook.

Recovery after treatment

A stent can remain in place long term if it functions and the situation is monitored. In a canine stent series, stents remained in place for up to 1,158 days. New narrowing or blockage may require stent replacement. Routine replacement is not needed for every patient.

Urine output can rise considerably after an obstruction is relieved. Fluid balance and electrolytes are monitored to prevent dehydration and excessive potassium loss. Severely elevated kidney values before relief predispose to greater post-obstructive urine output.

After treatment for kidney infection, blood and urine tests are usually checked 1–2 weeks after antibiotic treatment ends.

Prevention

Prevention is planned according to the stone's mineral composition. Diluting urine reduces conditions favouring stone formation. Water can be added to food, or wet food with over 75% moisture can be used. Identifying and treating urinary tract infection is central to preventing infection-associated struvite disease.

High blood calcium predisposing to calcium oxalate stones is corrected where possible. A low-purine diet may be selected to prevent urate stones. In androgen-dependent cystine stone disease, castration can prevent recurrence.

Dogs forming frequently recurring calcium oxalate stones usually have X-rays every 3–6 months. Composition-specific treatment aims to prevent encrustation of a long-term stent and new stones.

Important for dog owners

Know what is being monitored and when to seek care

Keep records of stone location and measurements, any mineral analysis, urine cultures and kidney values. Record changes in appetite, weight, vomiting, drinking and urination. Bring medication and diet details, and previous imaging results. Urine results, stone appearance and mineral composition affect treatment choice.

Ask whether the stone is already causing problems or is a finding to monitor. If your dog has a stent, agree how its function will be monitored and possible infection investigated. Establish which signs mean an immediate return for care. Typical bladder signs may be absent with ureteral obstruction. Do not delay seeking care because your dog is not straining to urinate. New vomiting, pain or deteriorating general condition needs assessment according to your emergency instructions.

Frequently asked questions

Must a kidney stone without signs always be removed?

No. Treatment is considered particularly for associated obstruction, recurrent infection, pain or kidney tissue compression. A finding causing no problems can be monitored with urine tests and ultrasound. Monitoring means planned checks, reassessing stone growth and any effect on urine flow.

Can kidney blood values be normal despite an obstruction?

Yes. With one-sided ureteral obstruction, the other kidney can compensate sufficiently to prevent azotaemia. The obstruction may then go undetected without imaging. Ureteral assessment therefore also uses ultrasound and the overall findings; a normal blood test does not exclude local kidney damage.

Can a dog's kidney stone be dissolved?

A kidney stone consistent with struvite can be dissolved if urine drainage is secure. An estimated 20–30% of canine upper urinary tract stones are struvite. Calcium oxalate stones do not dissolve. Treatment of urate and cystine stones is assessed separately.

What is a ureteral stent?

It is a tube placed inside the ureter that lets urine pass from the kidney to the bladder around an obstruction. A stent can remain in place long term. Its function and possible new stones are monitored, as new narrowing or blockage can require further treatment.

Why does a dog still receive fluids after an obstruction is relieved?

Urine output can increase considerably after relief. Without close fluid and electrolyte monitoring, your dog can become dehydrated or blood potassium can fall too low. Further care therefore depends on measured urine output and blood tests, rather than only on whether the obstruction was successfully bypassed.