Urinary Crystals in Cats: What, Why, and Prevention

For most cat owners, cat urine is one of the least desirable features of the human/cat arrangement. Yet for your cat’s health and well-being as well as your peace of mind, it’s imperative you understand how to provide the diet and care to keep your cat’s urinary system functioning optimally.

Feline Lower Urinary Tract Disease (FLUTD) refers to a host of diseases that can develop in your cat’s bladder and urethra. One common cause of FLUTD is urinary crystals, the two most common types being struvite and calcium oxalate crystals. With an overview of how
these urinary crystals develop and are diagnosed, you will be better prepared to provide your cat its best chance at a healthy, happy life free from lower urinary tract disease.

What Are Feline Urinary Crystals and Stones (Uroliths)?

Feline urinary crystals are collections of mineral molecules. These range from microscopic to large collections of crystals that become stones called uroliths. When uroliths develop in the kidneys, bladder ureters (tubes from kidneys to bladder), or urethra, the condition is called urolithiasis.

Factors of Crystals in Cats

Nutrition is the most important factor in crystal and urolith development in feline urinary tracts.[i] Dr. Jeffrey Judkins, DVM, of Animalkind Holistic Veterinary Clinic in Jacksonville, Oregon, explains diet contributes to feline urolith formation in three ways.

  1. First, dry diets cause cats to become dehydrated. Dr. Judkins says that “When this occurs, the urine produced by the cat becomes overly concentrated (high specific gravity). This, in turn, increases the concentration of minerals present in the urine and increases the likelihood of stone formation.”
  2. Second, Dr. Judkins points out that urine pH is central to urolith development. “An abnormally high urine pH predisposes cats to form struvite crystals and uroliths. Raw meat diets are, in general, higher in protein than dry cat diets, which results in a lower urine pH.”
  3. Finally, Dr. Judkins notes “there is considerable research linking chronic inflammation and a tendency towards urolith formation. Inflammation in the urinary tract predisposes the formation of the protein matrix, or nidus, which urinary stones form around.  Dry cat diets generally contain high levels of carbohydrates, which when consumed on a long-term basis, leads to a chronic, systemic inflammatory state. This is probably the underlying cause of a wide range of chronic inflammatory and metabolic diseases in cats, besides urinary stones.”[ii]

Dr. Judkins’ second point on urine pH is critical to a broader understanding of how feline uroliths have changed. Struvite crystals form in alkaline urine (high pH). To prevent struvite crystals, cat food companies developed commercial diets formulated to produce more acidic urine as early as the 1980s. Those food changes precipitated a noticeable increase in what were once rare oxalate uroliths. Oxalate uroliths went from being 1.5% of recovered uroliths in 1984 to 24% by 1992.[iii] By 2002, that figure increased to around 55%.[iv] Struvite cases dropped concomitantly to oxalate increases. Currently, by most accounts, struvite and oxalate uroliths occur in similar percentages, although Merck Veterinary Manual cites that “calcium oxalate uroliths are the most common feline uroliths.”[v],[vi]

Commercial food changes, unfortunately, have led to more surgeries to remove calcium oxalate stones, for this type of urolith requires surgical intervention. Struvite uroliths, on the other hand, depending upon their location, may be dissolved over time with dietary change and/or flushed out. (However, a struvite plug is in the urethra in the tubes connecting the kidneys to the bladder,so it will have to be removed surgically.)[vii]

Types of Feline Urinary Crystals

Struvite Crystals:

  • Struvite crystals are composed of magnesium, ammonium, and phosphate.
  • Struvite crystals are caused by too little water and consumption of dry food, which cause a cat’s urine to become too alkaline. Highly concentrated urine at or near a pH of 7 gives struvite crystals an optimal environment in which to develop.
  • The most serious struvite uroliths are urethral plugs, which if not caught in time can block all passing of urine and lead to a cat’s death within 24-48 hours.[viii],[ix] Male (especially neutered male cats) are at an especially high risk from urethral obstruction, for their urethras are longer and narrower.
  • Dry food diets with a moderate protein content that are “high in magnesium, phosphorus, calcium, sodium, chloride, and fiber” are associated with increased risk of developing struvite uroliths.[x]
  • Cats between the ages of 2 and 7 years of age show the greatest risk of developing struvite uroliths.[xi]
  • Female cats develop struvite uroliths more often than male cats.[xii]

Calcium Oxalate Crystals:

  • One key cause of an increased prevalence of oxalate crystals has been more acidifying food formulas, causing the urine to be at a more acidic pH. Calcium oxalate stones grow in more acidic urine because calcium oxalate is less soluble in acidic urine when compared with alkaline urine.[xiii]
  • Oxalate crystals are more likely to occur when high calcium levels are present in the blood. High blood calcium levels, which present in urine, can result from an excessive intake of calcium, protein, sodium, or vitamin D.
  • Because of the high acidity of the urine, cats with oxalate uroliths tend not to have bladder infections.
  • Older cats (ages 8 to 14 years old) are at greatest risk of developing oxalate uroliths.
  • Male cats more than female cats tend to develop oxalate uroliths.[xiv]
  • Breeds at an increased risk of developing oxalate uroliths are Persian, Himalayan, and Burmese.[xv]
  • Oxalate uroliths don’t dissolve with diet, but diet has a role in preventing their development. Once oxalate uroliths develop, they can really only be removed surgically.

Symptoms of Feline Urinary Tract Disease

It can be difficult to determine when something ails your cat, and it is especially hard if the cat has outdoor access and prefers to eliminate outdoors. Even so, here is a standard list of behaviors that may indicate the presence of FLUTD:

  • Urinating outside the litter box, especially in places like a tub or cool tile floor.
  • Straining when urinating, taking a long time to urinate, and urinating frequently.
  • Urinating small amounts.
  • Crying when urinating.
  • Excessive grooming of genital area

Things to Know About FLUTD Diagnoses and Treatment

The more observed behaviors you can report to your veterinarian, the better. Know, though, that the presence or absence of urinary crystals is only one aspect of diagnosing FLUTD.

  • Crystals can form in urine outside the body within 20 to 30 minutes, so home samples are unreliable as are tests for pH levels.
  • To diagnose a struvite urolith, your veterinarian may wish to augment a urine analysis with an X-ray or ultrasound before prescribing a dissolving regimen.
  • Cats with oxalate uroliths tend to not have crystals in their urine, so your veterinarian’s use of physical examinations, ultrasounds, and X-rays is particularly important.
  • Treatment depends on the type of urolith diagnosed as well as your cat’s other health considerations.
    • Oxalate uroliths require surgery.
    • Struvite uroliths, depending upon location, may be surgically removed or dissolved with diet. Struvite stones in female cats are more easily flushed with sterile fluids; sometimes veterinarians use cystoscopes to remove smaller struvite stones.[xvi]

Prevention Is Key!

You are your cat’s best opportunity for living a healthy and happy life free from the misery of FLUTD. The best research tells us that proper nutrition prevents most cases of struvite uroliths, and for oxalate uroliths, good nutrition certainly plays a preventive role. Above all, “feeding diets high in moisture is one of the cornerstones of urolith prevention.”[xvii] Here are things you can do immediately to prevent FLUTD:

  1. Have several water dishes with fresh water available for your cat. Because cats like running water, you may want to invest in a cat bubbler or drinking fountain. Here is a review of several: Best Cat Water Fountain: What to Look for in a Cat Drinking Fountain
  2. Make sure your cat’s water sources are in low-stress, cat-dominated areas.
  3. Make sure your cat gets exercise and maintains a healthy weight.
  4. Feed your cat several small meals throughout the day. By doing so, you not only replicate wild cat habits but also keep your cat’s pH in a more normal range, because urine tends to become more alkaline after a big meal.
  5. Follow the “have one more litterbox than you have cats” rule. Make sure the litter box is in a calm, safe area of the house. Clean it twice daily, and change the litter at least weekly or more often if your cat demands it.
  6. Try to minimize routine changes for your cat.
  7. Feed your cat a high-moisture, raw meat diet that is mildly acidic with the proper fats and nutrients. Cats need low-carbohydrate diets with a proper balance of fats. Cats have not evolved to tolerate carbohydrates, and grain fillers in most cat foods promote urine that is too alkaline. Dr. Jeffrey Judkins’ DVM prefers a raw diet to maintain long-term feline health. Although cats vary in their tastes, one thing is for sure, Dr. Judkins DVM ensures “cats with a history of urine stones are never allowed to eat dry food diets again.”[xviii]

Darwin’s Raw Cat Food is gluten free, grain free, and carefully formulated and tested to meet AAFCO feline nutritional profiles for all Life-Stages and the National Research Council’s guidelines for cat nutrition. It’s the best you can do for your cat’s urinary health. It’s the best you can do for your cat.


[i] M. T. Tion, J. Dvorska, and S. A. Saganuwan, “A Review on Urolithiasis in Dogs and Cats,” Bulgarian Journal of Veterinary Medicine Vol. 18, No. 1 (2015): Accessed December 16, 2017. http://www.uni-sz.bg/bjvm/BJVM-March%202015%20p.1-18.pdf. [ii] Jeffrey Judkins, DVM, “Response to Questions on Feline Uroliths,” Email. February 26, 2018. [iii] Tony Buffington, C.A. “Lower Urinary Tract Disease in Cats—New Problems, New Paradigms.” Journal of Nutrition Vol. 124, No. 26435. MasterFile Premier, EBSCOhost (accessed December 13, 2017). [iv] Vachira Hunprasit, DVM, et.al. “Canine and feline urolith epidemiology: 1981-2013,” DVM360 (Aug 01, 2014). Accessed December 13, 2017. http://veterinarynews.dvm360.com/canine-and-feline-urolith-epidemiology-1981-2013?pageID=3 [v] Scott A. Brown, VMD, PhD, DACVIM, Josiah Meigs, “Urolithiasis in Small Animals, Calcium Oxalate Stones,” Merck Veterinary Manual, Online Edition. Accessed December 16, 2017. https://www.merckvetmanual.com/urinary-system/noninfectious-diseases-of-the-urinary-system-in-small-animals/urolithiasis-in-small-animals [vi] Cathy Langston, DVM, DACVIM, et. al., “Diagnosis of Urolithiasis,” Compendium, Internal Medicine (August 2008) Vol. 30, No. 8 at VetFolio. Accessed December 17, 2017. http://www.vetfolio.com/diagnostics/diagnosis-of-urolithiasis [vii] “Urinary Tract Stones (Struvite) in Cats,” PetMD, Accessed December 16, 2017. https://www.petmd.com/cat/conditions/urinary/c_ct_urolithiasis_struvite?page=2 [viii] It should be noted that in 2010, sterile struvite uroliths, which result largely from diet, comprised about 90% of urethral plugs submitted to the Minnesota Urolith Center. See Jody P. Lulich, DVM, PhD, DACVIM, Carl A. Osborn, DVM, Phd, DACVIM, “Feline Urethal Plugs: 2010, a look at composition provides insight into ways to prevent plugs in the first place,” DVM360 (August 1, 2011). Accessed December 14, 2017. http://veterinarynews.dvm360.com/feline-urethal-plugs-2010 [ix] “Feline Lower Urinary Tract Disease,” Cornell Feline Health Center, Cornell University College of Veterinary Medicine. Accessed December 16, 2017. http://www.vet.cornell.edu/fhc/health_information/LowerUrinaryTractDisease.cfm [x] C. Lekcharoensuk, C.A. Osborne, J.P. Lulich, et al., “Association between dietary factors and calcium oxalate and magnesium ammonium phosphate urolithiasis in cats,” JAVMA (2001) 219: 1228-1237, cited in Gregory F. Grauer, DVM, MS, Diplomate ACVIM, “Feline Struvite and Calcium Oxalate Urolithiasis,” Today’s Veterinary Practice (September/October 2015): Vol. 5, No. 5. Accessed December 16, 2017. http://todaysveterinarypractice.navc.com/feline-struvite-calcium-oxalate-urolithiasis/ [xi] Gregory F. Grauer, DVM, MS, Diplomate ACVIM, “Feline Struvite and Calcium Oxalate Urolithiasis,” Today’s Veterinary Practice (September/October 2015): Vol. 5, No. 5. Accessed December 16, 2017. http://todaysveterinarypractice.navc.com/feline-struvite-calcium-oxalate-urolithiasis/ [xii] Ibid. [xiii] Amanda Callens, Joseph W. Bartges, “Update on Feline Urolithiasis,” August’s Consultations in Feline Internal Medicine (2016): Vol. 7. Excerpt available at “Calcium Oxalate,” Science Direct. Accessed December 14, 2017. https://www.sciencedirect.com/topics/veterinary-science-and-veterinary-medicine/calcium-oxalate [xiv] Grauer, “Feline Struvite and Calcium Oxalate Urolithiasis.” [xv] Ibid. [xvi] “Feline Lower Urinary Tract Disease,” Cornell Feline Health Center, Cornell University College of Veterinary Medicine. [xvii] J.P. Lulich, et. al., “ACVIM Small Animal Consensus Recommendations on the Treatment and Prevention of Uroliths in Dogs and Cats.” Journal of Veterinary Internal Medicine (2016): Vol. 30, No. 5: 1564–1574. PMC. Web. Accessed December 14, 2017. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5032870/ [xviii] Jeffrey Judkins, DVM, “Response to Questions on Feline Uroliths,” Email. February 26, 2018.