Chronic Kidney Disease (Chronic Kidney Failure) is one of the most common conditions in cats. Although it affects cats of all ages, the probability of developing it doubles from 7 years of age.
While the condition can be managed and its progression can be slowed down by maintaining a kidney-friendly diet and using medication, the earlier it is spotted the higher the chance that a cat will live longer and have a good quality of life.
Unfortunately, in most cases this disease is detected when at least 70% of the functional nephrons have been lost. The reason for it is that before that point it usually doesn’t manifest in symptoms.
Therefore, it is crucial to monitor a cat’s health and see a veterinarian for a cat’s health check up at least once a year. It may be beneficial to have more frequent check ups for the cats who are older than 7.
CKD is a chronic condition, but in some cats it does not progress when the correct diet is maintained.
While the condition can be managed and its progression can be slowed down by maintaining a kidney-friendly diet and using medication, the earlier it is spotted the higher the chance that a cat will live longer and have a good quality of life.
Unfortunately, in most cases this disease is detected when at least 70% of the functional nephrons have been lost. The reason for it is that before that point it usually doesn’t manifest in symptoms.
Therefore, it is crucial to monitor a cat’s health and see a veterinarian for a cat’s health check up at least once a year. It may be beneficial to have more frequent check ups for the cats who are older than 7.
CKD is a chronic condition, but in some cats it does not progress when the correct diet is maintained.
Diagnosis
Not only CKD is asymptomatic before 70% of nephrons are destroyed, it may not be apparent when a simple the blood test is performed.
For example, urea will be significantly increased only when there is a 60-70% decrease in kidney function; moreover, urea levels are also affected by diet, exercise and muscle mass.
Another routine test is for serum creatinine, results may be affected by diet, exercise and muscle mass, but to a lesser degree. This test may not be helpful unless the damage is less than 60%.
The test that is considered the most helpful in diagnosing CKD in early stages is SDMA (symmetric dimethylarginine). SDMA levels raise comparatively early, when there is only a 25% kidney damage. It is recommended to perform this test in all cats after the age of 7 during the regular check ups.
Levels of phosphorus and calcium are checked if CKD is suspected. High phosphorus level indicates that the damage of the kidneys may be severe.
Urealysis (urine testing) will show if there is protein loss through the urine. Urinary protein : creatinine ratio is estimated to assess proteinuria.
Ultrasonography is usually performed to estimate the amount of damaged tissue in kidneys, as well as tumors, abscesses, cysts, etc.
Radiography is used in some cases. This way stones and tumors may be spotted.
Another routine test is for serum creatinine, results may be affected by diet, exercise and muscle mass, but to a lesser degree. This test may not be helpful unless the damage is less than 60%.
The test that is considered the most helpful in diagnosing CKD in early stages is SDMA (symmetric dimethylarginine). SDMA levels raise comparatively early, when there is only a 25% kidney damage. It is recommended to perform this test in all cats after the age of 7 during the regular check ups.
Levels of phosphorus and calcium are checked if CKD is suspected. High phosphorus level indicates that the damage of the kidneys may be severe.
Urealysis (urine testing) will show if there is protein loss through the urine. Urinary protein : creatinine ratio is estimated to assess proteinuria.
Ultrasonography is usually performed to estimate the amount of damaged tissue in kidneys, as well as tumors, abscesses, cysts, etc.
Radiography is used in some cases. This way stones and tumors may be spotted.
Diet
Diets designed for CKD delay onset of uremic crisis and extend survival in dogs and cats with CKD stages 2–4. The diet should be highly-palatable, as cats have a tendency to develop anorexia.
Homemade diets may be more palatable for some cats, but must be created strictly according to the recipe created by a veterinary nutritionist.
Homemade diets may be more palatable for some cats, but must be created strictly according to the recipe created by a veterinary nutritionist.
Protein
Protein consumption does not impair kidney function, nor does it cause kidney damage. While historically protein consumption was thought to be a contributing factor to renal impairment in cats with CKD, this theory has been disproven. (See the studies in the end of this article.)
The reason protein restriction is recommended in cats with CKD is not its effect on the healthy kidney tissue, but the fact that waste products of protein digestion accumulate in blood due to the low function of the kidneys. This way high-protein consumption will exacerbate clinical signs by leading to azotemia in animals with advanced renal failure.
At the same time, in cats in early stages of CKD protein restriction may lead to hypoalbuminemia and weight loss. One of the reasons for that is low palatability of low-protein food.
Deciding on protein intake for dogs and cats with chronic renal failure depends on clinical signs and renal function impairment. Feeding the highest protein level that improves symptoms and manages blood urea nitrogen is recommended. Considering higher protein needs and inability to adapt to low-protein diets in cats is important. A combination of digestible, biologically valuable protein sources like eggs, dairy products, soy protein isolates, and some lean meats is preferred.
The reason protein restriction is recommended in cats with CKD is not its effect on the healthy kidney tissue, but the fact that waste products of protein digestion accumulate in blood due to the low function of the kidneys. This way high-protein consumption will exacerbate clinical signs by leading to azotemia in animals with advanced renal failure.
At the same time, in cats in early stages of CKD protein restriction may lead to hypoalbuminemia and weight loss. One of the reasons for that is low palatability of low-protein food.
Deciding on protein intake for dogs and cats with chronic renal failure depends on clinical signs and renal function impairment. Feeding the highest protein level that improves symptoms and manages blood urea nitrogen is recommended. Considering higher protein needs and inability to adapt to low-protein diets in cats is important. A combination of digestible, biologically valuable protein sources like eggs, dairy products, soy protein isolates, and some lean meats is preferred.
Phosphorus restriction is necessary
As chronic renal failure advances, the decline in glomerular filtration rate (GFR) results in reduced phosphorus excretion. Also, both the synthesis of calcitriol (active vitamin D) and the breakdown of parathyroid hormone (PTH) becomes impossible due to impaired kidney function. These changes disrupt phosphorus and calcium metabolism, potentially leading to hyperphosphatemia, osteodystrophy (bone demineralization), and the deposition of calcium phosphate crystals in soft tissues.
The accumulation of calcium and phosphorus in renal tissue triggers inflammation, scarring, and subsequent nephron loss. Consequetly, restricting dietary phosphorus may aid in managing renal secondary hyperparathyroidism, reducing mineralization, and minimizing damage to the remaining functional nephrons. This approach ultimately slows the progression of renal disease.
In some cats a restriction of dietary phosphorus may not be enough to prevent hyperparathyroidism. In that case phosphate binders, calcium and calcitriol supplementation may be necessary.
The accumulation of calcium and phosphorus in renal tissue triggers inflammation, scarring, and subsequent nephron loss. Consequetly, restricting dietary phosphorus may aid in managing renal secondary hyperparathyroidism, reducing mineralization, and minimizing damage to the remaining functional nephrons. This approach ultimately slows the progression of renal disease.
In some cats a restriction of dietary phosphorus may not be enough to prevent hyperparathyroidism. In that case phosphate binders, calcium and calcitriol supplementation may be necessary.
Omega-3 controversy
Hyperlipidemia has been shown to be causally linked to the progression of chronic renal disease in dogs and other species.
Opting for unsaturated fatty acids within the omega-3 category, such as specific fish oils and flax seed oil, might be the favored choice due to the positive impact these fatty acids can have on intrarenal hemodynamics and inflammation. Including omega-3-rich diets could potentially contribute to slowing down the progression of this disease in cats. BUT, according to the 2013 study, supplementation with Omega-3 has a potential to cause adverse reactions, such as altered platelet function, gastrointestinal adverse effects, detrimental effects on wound healing, lipid peroxidation, potential for nutrient excess and toxin exposure, weight gain, altered immune function, effects on glycemic control and insulin sensitivity, and nutrient-drug interactions.
According to the current data, omega-6 supplements need to be avoided in cats with CKD. Supplementation with omega-3 may be beneficial, but can cause adverse reactions, therefore it is important to consider the risks before including omega-3 supplements into the diet.
According to the current data, omega-6 supplements need to be avoided in cats with CKD. Supplementation with omega-3 may be beneficial, but can cause adverse reactions, therefore it is important to consider the risks before including omega-3 supplements into the diet.
Fermentable fiber
Adding fermentable fiber to the diet helps to decrease the amount of nitrogenous products in the blood and urine by partly redirecting them to the colon and subsequently into the fecal matter.
The mechanism is quite interesting. Feeding fermentable fiber (beet pulp, FOS, gum Arabic blend was used) causes bacterial growth in the large intestine and increases the activity of the bacteria. The bacteria synthesize the enzyme urease, which converts urea to ammonia and carbon dioxide. The ammonia is subsequently used by bacteria as a source of nitrogen for protein synthesis. This process functions to remove urea nitrogen from circulation and incorporate it into bacterial protein, which is then excreted via the feces.
The results of the studies are promising. By adding fermantable fiber, it becomes possible to increase the amount of protein in the diet of a cat with CKD without the risk of raising blood nitrogen.
The mechanism is quite interesting. Feeding fermentable fiber (beet pulp, FOS, gum Arabic blend was used) causes bacterial growth in the large intestine and increases the activity of the bacteria. The bacteria synthesize the enzyme urease, which converts urea to ammonia and carbon dioxide. The ammonia is subsequently used by bacteria as a source of nitrogen for protein synthesis. This process functions to remove urea nitrogen from circulation and incorporate it into bacterial protein, which is then excreted via the feces.
The results of the studies are promising. By adding fermantable fiber, it becomes possible to increase the amount of protein in the diet of a cat with CKD without the risk of raising blood nitrogen.
Sodium chloride (table salt)
Generally, sodium restriction is recommended as damaged kidneys may not be able to expel it efficiently and therefore there is a risk of sodium chloride accumulation. The accumulation of sodium may contribute to high blood pressure.
It is important to understand that decreasing sodium will not normalize the blood pressure as it is not the only factor at play.
Sources
- Canine and Feline Nutrition: A Resource for Companion Animal Professionals, 3rd Edition by Linda P. Case, Leighann Daristotle, Michael G. Hayek, Melody Foess Raasch, 2010;
- Lenox CE, Bauer JE. Potential adverse effects of omega-3 Fatty acids in dogs and cats. J Vet Intern Med. 2013 Mar-Apr;27(2):217-26. doi: 10.1111/jvim.12033. Epub 2013 Jan 16. PMID: 23323770;
- FELINE CKD. Diagnosis, staging and screening – what is recommended? by Dominique Paepe and Sylvie Daminet, 2013;
- Brown SA, Reinhart GA, Haag M, and others: Influence of dietary fermentable fiber on nitrogen excretion in dogs with chronic renal insufficiency. In Reinhart GA, Carey DP, editors: Recent advances in canine and feline nutrition, Iams nutrition symposium proceedings, vol 2, Wilmington, Ohio, 1998, Orange Frazer Press;
- Blackwell's Five-Minute Veterinary Consult: Canine and Feline 7th Edition by Larry P. Tilley, Francis W. K. Smith Jr., Meg M. Sleeper, Benjamin M. Brainard;
- Canine and Feline Nutrition and Dietetics: A Guide for the General Practitioner by Debora Guidi, 2020.
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