Bladder stones in dogs: symptoms, tests and treatment

Overview

A urinary stone is not the same as an individual crystal seen in a urine sample. Crystals are small structures, whereas a stone is a larger deposit formed by material accumulating together. Crystals may be present without actual stone disease, and dogs can also have stones without crystals being detected in a sample.

Stones are named according to their composition. Struvite and calcium oxalate stones are common in dogs; urate and cystine stones also occur. Different compositions require different treatment and prevention. This discussion focuses on bladder stones, but other parts of the urinary tract are also assessed when necessary.

Struvite stones have been estimated to account for about 50% of all urinary stones in dogs.

In one study from northern Europe, 52% of 2306 canine urinary stones analysed between 1982–2012 contained calcium oxalate. Struvite stones accounted for 37% of the same group. The proportions of stone types therefore depend on the dogs studied and the period examined.

Causes

In dogs, struvite stones are usually associated with a bacterial urinary tract infection. Certain bacteria alter urine composition and acidity in a way that makes crystallisation easier. Crystals can grow together into a layered stone with bacteria trapped inside. Changing the diet alone may then be insufficient, and the infection must also be treated.

The exact process by which calcium oxalate stones form is incompletely understood. The amount of calcium excreted in urine, inherited factors and nutrition may contribute. Some dogs have an underlying metabolic disorder that can be corrected.

Urate stones may result from an inherited problem with uric acid processing or abnormal blood flow through the liver. Cystine stones are associated with a kidney tubule disorder in which too much cystine is excreted in urine.

Struvite stones forming without bacterial infection are rare in dogs. An underlying cause may be a kidney tubule acid–base disorder that alters urine composition, for example.

A healthy dog's kidneys reabsorb about 97% of filtered cystine. In cystinuria, more remains in the urine, allowing this poorly soluble amino acid to precipitate into a stone.

Risk factors

Risk depends on the type of stone. Struvite stones are diagnosed more often in young, small female dogs, although other dogs can also develop them. Recurring urinary tract infection is a particularly important underlying factor in this group.

Calcium oxalate stones often occur in middle-aged and older dogs. Susceptible small breeds include Miniature Schnauzers, Bichon Frises, Yorkshire Terriers and Shih Tzus. Dalmatians have a recognised susceptibility to urate stones. Previous stone disease is also a reason for careful monitoring, as many types tend to recur.

Castrated males have a higher risk of calcium oxalate stones than entire males. Cystine stones, in contrast, are found mainly in young entire males.

Typical symptoms

Signs often resemble a urinary tract infection, and you cannot reliably distinguish the two at home. Some dogs have no signs, and stones may be found during investigations for another reason.

• Your dog asks to go outside more often than usual.

• Small amounts of urine are passed repeatedly.

• Your dog strains to urinate.

• Blood is visible in the urine.

• A previously house-trained dog has urinary accidents indoors.

Bladder stones can also cause abdominal discomfort.

Vomiting, abdominal pain and marked tiredness alongside difficulty urinating may indicate a more serious blockage.

A stone in the urethra can cause urine to dribble rather than flow in a normal stream. Stones in a ureter, which carries urine from a kidney to the bladder, can also be associated with reduced appetite.

Complications and consequences

A stone can enter the urethra and prevent the bladder from emptying. Urinary obstruction is an emergency in which the bladder can become damaged or rupture. The blockage can also be associated with abnormal heart rhythms.

Recurrence is a common problem, particularly with calcium oxalate stones.

Procedures carry their own risks, such as infection and narrowing of the urinary tract. Risk depends partly on which section of the urinary tract is involved in the procedure.

Stones lodge in the urethra more commonly in males than females. The male urethra narrows particularly at the penile bone, where stones often become trapped.

Without preventive treatment, cystine stones often recur within 1 year. Recurrence can also happen despite prevention.

Diagnosis at the vet

The vet asks about changes in urination, previous infections and stones, and your dog's diet. Large bladder stones can sometimes be felt during abdominal examination. Urinalysis assesses findings including inflammation and crystals. Bacterial culture and susceptibility testing help establish whether infection is present and which antimicrobial medicine may be needed.

X-rays and ultrasound establish the location, size and number of stones. Not every stone shows equally well on an ordinary X-ray, so one imaging method is not always enough. Ultrasound helps assess the bladder and upper urinary tract, but has limitations for examining the urethra.

A stone that has been removed or passed naturally should be analysed. Its composition guides both further treatment and prevention, and a single stone can contain several materials. Crystals in a sample do not always represent the whole stone's contents. Storage and the time before testing can also affect which crystals are seen, so follow the veterinary team's sampling instructions.

Blood tests can look for metabolic disorders predisposing to stones and take other diseases into account. For example, high blood calcium in a dog with calcium oxalate stones, or concurrent kidney or heart disease, can affect the plan.

A urate stone may prompt investigation of blood flow through the liver, particularly in a breed without a recognised inherited susceptibility. This may include measuring blood bile acids.

Stones that show poorly on X-rays can be investigated using contrast material introduced into the urinary tract through a catheter.

Treatment

The vet prescribes treatment according to the stone type and your dog's condition. A blockage is relieved urgently, without waiting for a diet to work. A catheter can sometimes move a urethral stone back into the bladder before further treatment.

Struvite stones can often be dissolved using a special diet. When stones are associated with infection, the urinary tract infection is treated at the same time. Other foods and treats can interfere with the aim of a therapeutic diet, so the whole family must follow the plan. However, dissolution is unsuitable for situations such as urethral obstruction, and other illnesses may limit use of the diet.

Complete dissolution of struvite stones takes an average of 1–2 months. Dissolution can also take 8–12 weeks or less than this. Urine and stone size are rechecked at about 4 weeks. If stones do not shrink within 1–2 months, they are unlikely to be struvite, and treatment is changed.

Calcium oxalate stones do not dissolve with medicines or dietary treatment, so they are physically removed when necessary. Options may include surgery or, in selected cases, endoscopy and stone fragmentation. Opening the bladder surgically is called cystotomy. The method depends partly on stone location and the procedures available.

Dissolution may be attempted for urate stones if they are not caused by liver disease. Treatment includes a vet-prescribed low-purine diet with a high water content and measures to make urine more alkaline. In Dalmatians, complete dissolution has succeeded in about half of cases in around 1 month.

Cystine stones can also be dissolved using a combination of a special diet and vet-prescribed medicines. If dissolution fails or urine flow is threatened, the stones are removed by a procedure.

A struvite dissolution diet is not always suitable for a dog with pancreatitis or markedly abnormal blood lipid levels. Surgical removal or stone fragmentation may be used instead.

Prevention

Increasing water intake and diluting urine help prevent many types of stone. Your vet may recommend wetter food or adding water to food. The diet is tailored to the stone type and other illnesses. Do not start supplements that alter urine acidity yourself, as different stones require different targets.

Recurrence of infection-related struvite stones is prevented by treating and monitoring urinary tract infections. Once infection has been treated, this stone type does not usually require a permanent special diet. In contrast, the underlying cause of struvite stones forming without infection may persist after the stones have disappeared.

In some males that form cystine stones, the disease depends on sex hormones, and castration may be recommended to reduce recurrence. However, not all cystinuria resolves this way. The decision depends on the confirmed stone type and your dog's individual circumstances; it is not a preventive measure for every dog with urinary stones.

For dogs at high risk of calcium oxalate stones or with repeated recurrences, X-rays are often taken every 3–6 months. Stones found while still small can sometimes be removed by a flushing procedure, avoiding another operation.

Important for dog owners

On walks, watch whether urine passes and what straining looks like. Record when signs began, any blood and accidents indoors. Do not assume that squatting or lifting a leg means the bladder has emptied. If you cannot tell whether urine is passing and your dog is in pain, seek prompt advice from the veterinary team.

At discharge, ask about the stone type, any remaining stones, the purpose of the diet and the next recheck. Appetite, general condition and urine flow are also monitored after surgery. Ask about wound care and use of a protective collar. Check how to contact the veterinary team in the evenings and at weekends if your dog's condition changes. Keep the stone analysis result, as it may also help in a future emergency.

Frequently asked questions

Are urinary crystals the same as urinary stones?

No. Crystals can appear in a sample without actual stone disease, and stones can be present without crystals being detected. Results are therefore assessed alongside signs and imaging. Do not start a long-term therapeutic diet yourself based solely on the name of a crystal.

Can every urinary stone be dissolved with food?

No. Struvite stones may be suitable for dissolution, but calcium oxalate stones do not dissolve this way. A blockage or another illness may also prevent dissolution treatment. The stone type and the patient's safety are assessed before diet becomes the main treatment.

Why is a stone sent to a laboratory?

Its composition guides further treatment and prevention of recurrence. A stone may contain several materials, which can explain a poorer dissolution response than expected, for example. Keep the analysis result and make sure the diet and recheck plan are updated accordingly.

Can stones come back after surgery?

Yes. Removal deals with the existing stone, but does not always address why it formed. Recurrence is a significant problem with calcium oxalate stones in particular. Agree monitoring tests before discharge so a new stone can be found as early as possible, before serious signs develop.

Can a urinary blockage wait until morning?

Do not wait if your dog strains but passes no urine. A blockage is an emergency that can be life-threatening. Call an emergency vet and mention any vomiting, pain or tiredness too. Starting a therapeutic diet at home will not relieve a blockage.