Apatite stones in dogs

Apatite or calcium phosphorous stones are the least common type of stone I see in practice. These rare stones form from the same risk factors responsible for calcium oxalate stones. These include increased amounts of calcium and/or phosphate in the urine. The one big difference is pH. While calcium oxalate stones precipitate out of acidic urine, calcium phosphate stones form in urine with an increased or basic pH. This increased pH may be caused by urease producing bacterial infections.
The same breeds that show an increased incidence of calcium oxalate are also prone to calcium phosphate stones. In addition to miniature schnauzers, Yorkshire terriers, shih tzu and miniature poodles, cocker spaniels are also on this list. Since females are more prone to urinary tract infections, they tend to have more calcium phosphate stones.

Treating calcium phosphate stones is tough because they often form in the kidney. Since surgical extraction will damage the kidney, I usually recommend lithotripsy for this condition. More information on lithotripsy may be found at my blog post; Removing Urinary Stones With Lithotripsy in Dogs. Once the stones are gone, prevention is based on keeping the urine dilute to flush the crystals out before they can form stones. Giving urinary acidifiers is not recommended as it might cause the formation of calcium oxalate stones.  


-Shell, Linda. Urolithiasis, Calcium Phosphate. Canine Partner, VIN 3/1/2010.

Published by kristennelsondvm

Dr. Kristen Nelson grew up on a farm in Watertown, Minn., where she developed a deep love for animals of all kinds. She received a Doctor of Veterinary Medicine degree from the University of Minnesota, College of Veterinary Medicine. Kris then completed a small-animal internship at the prestigious Animal Medical Center in New York City. In addition to writing and speaking, she cares for small and exotic animals in Scottsdale, Az. Dr. Nelson is widely quoted in the media. Her credits include Ladies’ Home Journal, USA TODAY, the Los Angeles Times and numerous radio and television interviews. Dr. Nelson has written two books, Coated With Fur: A Vet’s Life and Coated With Fur: A Blind Cat’s Love. Kris and her husband Steve share their home with rescued cats, birds and a dog.

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