Calcium Deposits in the Urinary Tract in Dogs

Various mineral deposits can form stones in the bladder or kidneys of dogs. These stones are called uroliths or sometimes calculi. As they move through the urinary tract, they often become stuck in the one of the ureters, between the kidneys and the bladder, or in the urethra, below the bladder. Calcium oxalate is the second most common urolith in dogs. These types of stones are more likely in male dogs and their incidence has increased since the early 1980’s. A number of factors can influence their development, including high levels of calcium or oxalate in the diet, water consumption, and genetic or breed factors. If the stones are too large to pass through the ureter or urethra, they must be surgically removed. There is currently no chemical method of breaking up the stones, since any compound strong enough to dissolve them would be harmful to the body. Stones that entirely block the flow of urine can cause uremia (blood toxicity) and fatal kidney damage if they are not treated quickly. Bacteria commonly hide in the stones and may cause serious urinary tract infections. Dogs have a good chance of recovery if the stones are removed successfully. Dietary changes may be necessary to avoid recurrence.

High calcium levels in the urine of dogs can lead to mineral deposits and stones in the urinary tract. Stones can cause urinary blockage and increase the risk of infection. Veterinarians define this condition as canine urolithiasis. Stones made of calcium oxalate are very hard and usually need to be surgically removed.

Stones in the bladder or kidneys are often asymptomatic, but in the ureter or urethra they will cause pain and urinary difficulty. With a severe blockage, life-threatening symptoms can develop quickly, so seek veterinary treatment as soon as possible.

• Painful urination (dysuria)
• Reduced or difficult urination (stranguria)
• Frequent attempts to urinate
• Blood in the urine (hematuria) 
• Repeat urinary tract infections
• Abdominal pain
• Abdominal distention or bloat
• Vomiting
• Lethargy
• Weakness

Types

Calcium is one of a number of minerals that forms uroliths in dogs. Since any type of stone can cause similar symptoms, you may not be able to tell immediately which type your dog has. These are some of the uroliths found in dogs.

• Struvite stones – made of struvite, this is the most common type, found mainly in female dogs
• Calcium oxalate stones – the second most common type, calcium and oxalate bind together to form a very hard stone, found mainly in male dogs
• Urate stones – made of ammonium urate, the next most common type after calcium oxalate

Calcium and oxalate are normally found in the urine. When these levels increase however, hypercalciuria develops. This is usually a precursor to stone formation. Many conditions can lead to high calcium levels in the urine

• High calcium content in the diet
• Eating foods that produce oxalate or increase urine acidity
• Excessive calcium excreted from the kidneys - it’s not known what causes this
• Hypercalcemia – large amounts of calcium released into the blood from skeletal deposits (this rarely leads to stones)Lack of fluids

The reason for stone development is not fully understood. Under the same conditions, some animals will develop stones while others will not. The following conditions increase the risk of calcium oxalate stones.

• More common in smaller dogs
• More common in some breeds:Bichon Frisé, Miniature Schnauzers, Lhasa Apsos, Yorkshire or Cairn Terriers, Shih Tzus, Miniature Poodles, Pomeranians, Maltese, Keeshonds
• More common in male dogs
• More common in dogs between 5 and 9 years old

Based on your dog’s symptoms, the veterinarian will suspect some type of urinary blockage. Some stones are large enough to be felt during a physical examination. This may be more difficult if your dog is in a lot of pain. Stones can cause bladder infection and the area may be swollen and hard.

Further testing will be necessary to make a definitive diagnosis. X-rays can usually show the stone’s exact placement. In some cases, if stones are located in the kidneys and there are no symptoms, they may be discovered on an x-ray for an unrelated cause. Urine tests can usually show what type of stone your dog has. Blood is present in the urine with most uroliths. With calcium oxalate stones, however, the urine will also be very acidic (with a PH below 6.5). It will have a high calcium content and, in many cases, small calcium oxalate crystals will also be present. High levels of white blood cells in the urine may also indicate the presence of infection. This commonly forms secondary to calcium oxalate stones.

The veterinarian will want to know your dog’s medical history, especially any prior incidence of stones in the urinary tract. Family and breed history can also be relevant. Bloodwork will be done to check blood calcium levels and evaluate whether there is reduced kidney function.

Surgical removal is the most common treatment. Stones can be removed from the lower urinary tract with minimally invasive surgery. In some cases, the stones have a grainy nature with many small crystals embedded throughout the bladder. The veterinarian will attempt to flush all the grains out during surgery, but stones of this type have a high incidence of recurrence. Your dog will need to spend several days in a veterinary hospital to recover, and there will be a two to three week period of diminished activity after returning home. Antibiotics will be prescribed to limit infection.

If the stones are located in the kidneys, surgery can be more problematic. Removing kidney stones is a risky procedure that can result in permeant damage if it goes wrong. Many veterinarians will choose to manage the condition with antibiotics to limit infection and frequent testing. 

In some cases, other methods may be used to avoid surgery. Very small stones that are only just too large to be passed normally may be able to be flushed out in a process called urohydropropulsion. It’s also possible that cystoscopy (the insertion of an instrument to break up the stones) may be possible, but this is a specialist procedure that isn’t practiced by most veterinarians.

Many dogs will make a complete recovery once the stones are removed. The veterinarian may recommend diet changes to avoid recurrence. Extra fluids are the most important element since this greatly reduces mineral concentration in the urine. Feeding your dog wet, canned food rather than dry food is a good way to increase fluids. In some cases, the veterinarian may recommend a high sodium diet to encourage drinking, but this will depend on your dog’s other health issues. Reducing calcium and oxalate in the diet can also be effective, but these two elements need to be balanced carefully. This can be difficult since oxalate is mostly produced in the body rather than through ingestion. The veterinarian may suggest you avoid giving your dog certain foods. If your dog is on a reduced calcium diet, he should be monitored closely for nutritional deficiency.