What Are Urinary Crystals in Cats?
Urinary crystals are microscopic mineral deposits that form within a cat's urine when certain minerals become highly concentrated and precipitate out of solution. They are detected during laboratory analysis of a urine sample, specifically a process called urine sediment examination, in which the sample is centrifuged and examined under a microscope.
Finding crystals in a cat's urine is not automatically a cause for alarm — small numbers of certain crystal types can appear in healthy cats. However, when crystals are present in significant quantities, or when they are associated with symptoms, they require veterinary attention and management. Left unaddressed, crystals can progress to form stones, plug the urethra, and in male cats, cause a life-threatening urinary blockage.
The Two Main Types of Urinary Crystals
While several types of crystals can form in feline urine, the two that are encountered most commonly and that have the greatest clinical significance are struvite and calcium oxalate.
Struvite Crystals
Struvite crystals are composed of magnesium ammonium phosphate. They form in urine that is alkaline (high pH) and are the most common crystal type seen in cats. They are particularly associated with younger cats and with diets high in magnesium. One notable feature of struvite crystals and stones is that they can often be dissolved through dietary management alone, without the need for surgery. Prescription urinary diets that acidify the urine and restrict magnesium intake are effective at dissolving existing struvite crystals and stones and preventing new ones from forming.
Calcium Oxalate Crystals
Calcium oxalate crystals form in urine that is acidic (low pH). They have become increasingly common in cats over recent decades and are more frequently seen in older cats, particularly males of certain breeds including Burmese, Himalayan, and Persian cats. Unlike struvite, calcium oxalate crystals and stones cannot be dissolved through dietary management. If they progress to form stones of significant size, they typically require surgical removal — a procedure called a cystotomy — or, in specialist centres, techniques such as laser lithotripsy. Dietary management is used after removal to reduce the risk of recurrence, but the diet required differs substantially from that used for struvite.
How Crystals Are Detected
Urinary crystals are identified through urinalysis, specifically through examination of the urine sediment. Your vet will ask you to collect a fresh urine sample, ideally the first of the morning, in a clean sterile container. The sample is centrifuged to concentrate the sediment, which is then examined under a microscope. The type of crystal can usually be identified by its characteristic shape — struvite crystals appear as rectangular prisms, whilst calcium oxalate crystals have a distinctive envelope or dumbbell shape.
Imaging may also be used. X-rays can detect calcium oxalate stones, which are radiopaque (visible on X-ray), while ultrasound is useful for detecting bladder stones of various types and for assessing the condition of the bladder wall.
Symptoms: What to Watch For
Many cats with urinary crystals show no obvious symptoms, particularly if the crystals are small in number and not causing significant irritation. When symptoms are present, they typically reflect inflammation or obstruction of the urinary tract and may include:
- Straining when attempting to urinate
- Haematuria — blood in the urine, which may appear pink, red, or brownish
- Frequent visits to the litter tray, often producing only small amounts of urine
- Urinating outside the litter tray
- Licking the genital area more than usual
- Signs of pain or discomfort around the abdomen
In male cats, crystals contributing to a urethral plug or blockage will cause straining with no urine production, vocalisation in pain, vomiting, and eventually collapse. This is a medical emergency — go to an emergency vet immediately if your cat is producing no urine and is in distress.
The Risk of Stones and Blockage
Crystals themselves are small and may pass harmlessly in the urine. The concern arises when they accumulate and aggregate into larger formations. Crystals can bind together with mucus, inflammatory material, and protein to form urethral plugs, which can obstruct the urethra — particularly in male cats. Over time, crystals can also consolidate into solid mineral stones (uroliths) within the bladder or urethra, causing chronic irritation, bleeding, and in some cases obstruction.
Early identification and management of crystal formation is therefore important not just for managing current symptoms but for preventing these more serious complications.
Treatment: Struvite Crystals
For struvite crystals, the primary treatment is dietary. Your vet will typically prescribe a specialised prescription urinary diet, such as Royal Canin Urinary S/O or Hill's Prescription Diet c/d, that is formulated to acidify the urine and reduce the concentration of minerals that contribute to struvite formation. These diets are highly effective at dissolving struvite crystals over several weeks and at preventing recurrence with long-term feeding.
Increasing water intake is also central to management. Wet food is preferable to dry food as it naturally increases water consumption, producing more dilute urine in which crystal formation is less likely. Encouraging drinking through water fountains or multiple water stations is beneficial.
Treatment: Calcium Oxalate Crystals
Calcium oxalate crystals cannot be dissolved. If they have progressed to form bladder stones, surgical removal is typically required. Following surgery, long-term dietary management is needed to reduce recurrence. Prescription diets for calcium oxalate prevention differ from those for struvite — they aim to keep the urine at a neutral pH and reduce urinary calcium and oxalate levels. In some cases, urinary acidifiers or potassium citrate supplementation may be prescribed.
Increased water intake is equally important for calcium oxalate management, as dilute urine reduces the concentration of calcium and oxalate available to form new crystals.
What Not to Do: The Importance of Accurate Diagnosis
It is essential not to attempt to manage urinary crystals at home without a confirmed diagnosis and veterinary guidance. The dietary treatment for struvite and calcium oxalate are not interchangeable — in fact, feeding a diet designed to dissolve struvite can actively worsen calcium oxalate disease by acidifying the urine further, and vice versa. Without a urinalysis and ideally stone analysis confirming the crystal type, choosing the wrong diet could make the situation significantly worse.
Never purchase over-the-counter urinary supplements or home remedies for a cat showing urinary symptoms without first establishing the underlying diagnosis with your vet.
Monitoring and Recheck Schedule
Once a cat has been diagnosed with urinary crystals and treatment has begun, follow-up urinalysis is typically recommended at four to six weeks to assess the response to dietary management and confirm that crystal levels are reducing. For cats on long-term prescription diets, periodic urine checks — often every three to six months — allow early detection of any recurrence. Imaging may also be repeated to confirm stone dissolution or to screen for new stone formation.
When to Go to the Emergency Vet
Seek emergency veterinary attention immediately if your cat is making repeated attempts to urinate with no urine produced, if he is vocalising in pain, vomiting, extremely lethargic, or has collapsed. These signs indicate a possible urethral obstruction, which is life-threatening. A cat with a known history of urinary crystals or stones is at elevated risk for this complication, and any sudden worsening of symptoms should be treated as urgent.