When we’re looking at urine samples down the microscope, we often see pretty little patterns forming, like snowflakes or tiny jewels. Unfortunately, these bladder crystals can cause serious disease in dogs and cats – but the good news is that by looking at their shapes under the microscope, we can often determine how best to treat them.
What problems can bladder crystals cause?
The biggest issue is that crystals don’t often stay microscopic! Eventually they grow, forming stones in the bladder (uroliths). These irritate the bladder lining, causing cystitis. However, the biggest risk is that the crystals find their way down into the urethra (urine tube leading from the bladder to the outside world) and get stuck there, preventing the dog or cat from urinating.
This is uncommon in females, because their urethra is relatively short and wide, so anything that fits into it tends to be passed (possibly after some straining). In males, however, the urethra is long and narrow, so obstructions are much more likely. A blockage is particularly likely to occur where the urethra bends around the pelvis, or in the penis where the penis bone causes a dramatic narrowing. The highest risk of all is in tomcats which were neutered early – towards the end of puberty in cats the penis dramatically grows, with the urethra becoming much wider. If the cat was neutered before this growth phase occurs, the penis and urethra stay small for life.
What types are there?
There are a number of different types of crystal, so let’s look at them in turn…
Struvite
Also known as magnesium ammonium phosphate and triple phosphatcrystals.
Look like “coffin lids” – rectangular crystals.
Caused by:
- Alkaline urine
- Infection (in dogs only)
- Struvite crystals will often form in stale urine even in normal animals.
- The stones can be dissolved with a proper diet
Cystine
Look flat, thin and hexagonal, a bit like a snowflake.
Caused by:
- Acidic urine
- A genetic disorder resulting in kidney disease (seen in breeds such as Newfoundlands, Bassets, Chihuahuas).
- Can be dissolved with a suitable diet
Calcium Oxalate
Form small square crystals with an X in the centre.
Can form in alkaline or neutral urine.
Caused by:
- Genetic predisposition (e.g. Yorkshire Terrier and Lhasa Apso dogs; Burmese and Persian cats)
- Antifreeze poisoning
- Excessively high blood calcium levels (in conditions such as hyperparathyroidism, some tumours)
- Cannot be dissolved, must be surgically removed.
Urate
Also known as Ammonium Urate
Look like spikes or spindles, or occasionally spiky balls (“thorn-apples”).
Found in acidic and neutral urine.
Caused by:
- Normal in Dalmatians!
- Liver disease, such as a portosystemic shunt.
- Can be dissolved with a proper diet.
Uric Acid
Usually diamond shaped.
Pretty rare, occasionally occur in acidic urine.
Calcium Phosphate
Long, thin rectangular crystals
Quite rare, occur in alkaline urine.
Calcium Carbonate
Cause the urine to appear cloudy – normal in rabbits and horses!
What are the symptoms of bladder stones?
Cystitis
Blood in the urine
Pain on urination
Passing urine little and often
Bladder obstruction
Straining to urinate
Passing very little or no urine
Uraemia
Depression
Dehydration
Vomiting
Collapse
Death
How can they be treated?
Many stones can be dissolved in a suitable diet; if, however, they are causing an obstruction they must be removed surgically. This is usually done by opening the bladder and removing the stones. For stones lodged in the urethra, the preferred technique is retrograde urohydropropulsion, whereby we flush the stones backwards into the bladder.