You're here because your feline friend has been diagnosed with a calcium oxalate bladder stone, and you're on a quest for more knowledge. Your cat likely falls into one of three scenarios:
- Stone discovery during urinary discomfort investigation
- Identification during unresolved urinary tract infection assessment
- Incidental detection during unrelated examinations
Cats with bladder stones often exhibit classic feline lower urinary tract disease symptoms: straining while urinating, bloody urine, improper elimination, and genital licking. During symptom evaluation, a radiograph reveals one or more stones in the urinary bladder. Alternatively, a documented urinary tract infection prompts further investigation, leading to stone discovery. Or, the cat may remain asymptomatic, with stones unveiled through routine radiography.
In any instance, you're left with bladder stones and a mission: to remove them and prevent recurrence. The crucial starting point is determining the stone's type. While urinalysis offers some insight, retrieving a stone for analysis is pivotal. Though fortunate scenarios allow for passing small stones for lab analysis, surgery or other retrieval methods are often necessary. Unlike struvite stones, dietary manipulation won't dissolve calcium oxalate stones. Surgical intervention or stone retrieval methods become the primary options.
The Whys of Calcium Oxalate Stones
Around 25 years ago, calcium oxalate bladder stones were practically unheard of in cats. Struvite stones (ammonium-magnesium-phosphate matrix) were the norm. Feline lower urinary tract symptoms were primarily attributed to struvite crystals, prompting the pet food industry to acidify cat foods to inhibit crystal formation. The strategy succeeded—lower urinary tract symptoms decreased, especially in males prone to struvite urinary blockages. Yet, the flip side emerged: calcium oxalate bladder stones began emerging. Acidifying bodies result in acidic urine pH and elevated urinary calcium, both favoring calcium oxalate stone formation.
Presently, most feline bladder stones are calcium oxalate stones.
Navigating Calcium Oxalate
Certain breeds, like Burmese and Himalayan cats, appear genetically predisposed to calcium oxalate stones. Cats typically develop these stones between 5 and 14 years of age. Around 35% of cats with calcium oxalate bladder stones exhibit elevated blood calcium levels (hypercalcemia). These cats tend to lack bladder infections and display acidic urine pH on urinalysis. Obesity also contributes to calcium oxalate stone formation.
Stone Removal Strategies
- Cystotomy (Surgical Removal): Swift resolution involves surgical stone removal. The cat is anesthetized, the belly is incised, granting access to the bladder. Stones are extracted, cultures are taken, and the bladder is sutured. Post-surgery pain relief and antibiotics are standard. Hospitalization for observation is typical, accompanied by post-surgery blood in the urine.
- Cystoscopy: Less invasive, this method employs a cystoscope to extract small bladder stones via a basket-like accessory. For larger stones, laser lithotripsy breaks stones into smaller pieces for extraction or passage. Cystoscopy and laser lithotripsy are feasible only in female cats due to urethra size.
- Voiding Urohydropropulsion: For smaller stones, this method may work if they can pass through the urethra. The bladder is filled with fluid, agitated, and pressure-assisted manual expression expels stones. Gravity helps position stones for expulsion. Larger stones aren't suitable for this technique.
Steering Clear of Future Stones
Preventing subsequent calcium oxalate stones proves challenging. Elevated blood calcium levels (if present) should be addressed. For those with normal calcium levels, a stepwise approach is recommended:
Step One
Feed a non-acidifying diet that minimizes urinary calcium oxalates. This diet features regular calcium content, moderate magnesium content, and urinary calcium-binding citrate. Consult your veterinarian for suitable therapeutic food. Canned food is preferred due to its higher water content. Dilute urine and optimal urinary pH are essential, favoring canned food and controlled meal feeding.
Avoid vitamin C supplementation, as it converts to oxalic acid and, subsequently oxalate. Be cautious with pet vitamin supplements.
Perform a urinalysis in two to four weeks to verify the absence of calcium oxalate crystals, dilute urine (specific gravity < 1.020), and alkaline urine pH (6.8-7.5).
Step Two
Rectify issues from the first urinalysis. If specific gravity exceeds 1.020, it indicates inadequate urine dilution. Encourage water intake, primarily through increased canned food consumption. A drinking fountain or Purina Hydra Care® may help.
Reassess in two to four weeks.
Step Three
Address oxalate crystals, concentrated urine, or acidic urine pH (pH < 7.5). Add a thiazide diuretic to dilute urine and restore electrolyte balance. Consider supplementing with vitamin B6, which addresses oxalate stone development in certain cats. Adjust food if needed.
Regular follow-ups with urinalysis and radiography every three to six months (urinalysis) and six to 12 months (radiography) are recommended. Surgical removal might be possible for females with small stones, while males often require surgery due to narrower tracts.
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