What Is Cystinuria?
Cystinuria is an inherited defect in the kidneys. Normally, the kidneys filter amino acids (the building blocks of protein) out of the blood and then reabsorb them. In cystinuria, the kidney tubules fail to reabsorb cystine and a few related amino acids, so they spill into the urine. Cystine does not dissolve well in acidic urine, so it forms crystals and then hard cystine stones in the bladder, kidneys or urethra.
Cystinuria itself causes no symptoms. The problems come from the stones it produces.
Mostly a male-dog problem
Male dogs have a long, narrow urethra, so a small cystine stone can lodge there and block urine flow. Any male dog straining to pee with little coming out needs a vet the same day.
Breeds at Risk
- Dogs: English Bulldogs, Dachshunds, Newfoundlands, Labrador Retrievers, Mastiffs, Scottish Deerhounds, Irish Terriers, Basset Hounds, Chihuahuas and Australian Cattle Dogs, among others
- Cats: rare, but it does occur
- Some forms appear in young dogs of either sex; others are hormone-linked and mainly affect intact adult males
Signs of Cystine Stones
- Straining to urinate or frequent small amounts
- Blood in the urine
- Accidents in the house or licking the genitals
- Dribbling, or no urine at all if the urethra is blocked
- Vomiting, lethargy and pain in a blocked dog, which is an emergency
Diagnosis
Your vet will run a urinalysis, where flat, hexagonal cystine crystals are a strong clue, and take X-rays or an ultrasound. Cystine stones can be faint on plain X-rays, so ultrasound or contrast studies are often needed. Any stone that is removed should be sent for analysis, because the stone type decides the treatment. A urine test for cystine and DNA tests for some breeds can confirm cystinuria.
Treatment
- Removing stones: small stones may be flushed out or retrieved through a scope; larger ones need surgery. A blocked urethra is relieved first with a catheter.
- Dissolving stones: a low-protein, alkalinizing diet plus a medication that binds cystine (such as tiopronin) can dissolve some cystine stones.
- Neutering: in the hormone-linked form seen in intact males, neutering can stop or greatly reduce stone formation.
Preventing Stones Coming Back
Cystinuria is lifelong, so prevention is ongoing: a vet-prescribed diet that keeps urine less acidic, plenty of water (wet food or water added to meals helps), regular urine checks and imaging every few months, and medication when needed. For an overview of every stone type, see bladder stones in dogs and bladder stones in cats.
Frequently Asked Questions
Is cystinuria curable?
The underlying kidney defect is not curable, but stones can usually be controlled with diet, water intake and medication. Neutering can resolve the hormone-linked form in males.
Can cystine stones come back?
Yes. Without prevention, many dogs form new stones within a year, which is why regular rechecks matter.
Should I breed a dog with cystinuria?
No. Affected dogs, and carriers identified by DNA testing where a test exists, should not be bred.
If your dog is straining to urinate, find a veterinary clinic near you right away.