Nutritional management of chronic kidney disease in cats

Healthy kidneys are important for many vital roles within the body. Beyond elimination of nitrogenous waste products, hormones and drugs from the body, these roles include hormone production: renin and erythropoietin; Vitamin D activation; regulation of acid base balance, electrolytes and hydration.

Chronic kidney disease (CKD) is defined as ‘the presence of persistent functional or structural abnormalities of one or both kidneys’. CKD is the second most common cause of mortality in cats (12.1%) with at least 1 in 3 cats likely to develop some form of kidney disease in their lifetime [1]. Estimates range from 32% to 42% of cats over 12 years being affected [2].

Kidney disease can be initiated by any non-specific, single underlying disease process; when the resulting decreased renal function continues for at least 3 months, it is termed chronic. The initiating factor results in nephron loss and it becomes a self-perpetuating cycle of kidney injury. Microscopically CKD is typified by tubulointerstitial inflammation and fibrosis.

SDMA- symmetric dimethylarginine is a more specific marker of kidney function (glomerular filtration rate GFR) than traditional tests. SDMA detects >25% loss of kidney function compared to the >75% loss detected by creatinine [3]. Earlier detection provides increased opportunity for therapeutic intervention and possibly greater impact on outcome.

Staging

Full details on staging of CKD can be found:
http://www.iris-kidney.com/pdf/IRIS_Staging_of_CKD_modified_2019.pdf

Treatment

IRIS guidelines

http://www.iris-kidney.com/pdf/IRIS_CAT_Treatment_Recommendations_2019.pdf

Treatment must be tailored for the individual, but IRIS provides a solid starting framework to consider. Patients should be monitored, and treatment adjusted according to response. Treatments fall into two categories- those slowing the progression of CKD and preserving kidney function; those improving quality of life and addressing clinical signs.

For now, we shall focus on the nutritional aspect of management. IRIS currently recommends consideration of a renal diet for cats in stage 1 with proteinuria, and all cats in stage 2 or beyond.

Protein

Renal prescription diets have been the mainstay of management for cats with CKD for many years [4]. It has long been known that reducing protein reduces the clinical signs of uremia. Protein metabolites are usually excreted by the kidneys, but when kidney function is compromised, these metabolites accumulate and produce the clinical signs of uremia- anorexia, vomiting, depression, oral ulceration. Thus, reducing protein reduces the signs of uremia.

Researchers found that feeding a prescription renal diet (phosphate and protein-restricted) to cats with azotemic CKD improves survival and slows progression of disease [5] [6]. Hall et al found cats on a renal diet had a median survival time of 633 days versus 264 days.

Other studies have shown evidence that cats fed a renal diet had reduced azotemic crises, lower urea and phosphate levels and fewer renal related deaths than control cats fed an adult maintenance diet [7].

Phosphorus

Normal regulation of blood phosphate requires renal excretion. Diseased kidneys have a reduced capacity to excrete sufficient phosphate on a daily basis; this mechanism is thought to underlie the biochemical abnormalities of calcium-phosphate homeostasis, bone disease, and soft tissue calcification, collectively termed chronic kidney disease-mineral and bone disorder (CKD-MBD) [8].  However, beyond this, the exact mechanism through which phosphorous restriction positively affects CKD progression and survival is not fully understood. Recently studies have been focusing attention on the role of fibroblast growth factor 23 (FGF23) in phosphate regulation and CKD [9].

Phosphorus and protein content are not inextricably linked, but a major source of dietary phosphorus is protein; thus, limiting protein usually has the concurrent effect of limiting phosphorus. Another way to reduce phosphorus intake is administration of phosphorus binders, however giving unpalatable medications at every meal to cats with already reduced appetite, is a compromise on quality of life.

Other modifications

Whilst protein and phosphorus restriction are likely the key factors in the positive effects seen with a renal diet, the combination of multiple nutrient adjustments will be a major factor also. However further study is needed to fully evaluate and quantify this. Renal Diets are high in their fat content to increase energy density and also palatability.

Renal diets are formulated to help prevent development of metabolic acidosis which in turn helps prevent the development of hyperphosphatemia.

Antioxidants are included in many renal diets; these reduce renal oxidative stress, thought to contribute to progression of renal disease. In addition, omega 3 FAs (eg EPA) have been found to have renoprotective properties [10]. Soluble fibre (eg Psyllium) will help to bind gastrointestinal toxins such as urea and eliminate them in faeces.

Early CKD- stage 1

Until recently clinicians have rarely been identifying cats with non-azotemic early CKD and so the effect of dietary management and precise dietary recommendations have yet to be elucidated.

With the advent of new more sensitive and specific testing (SDMA), more cats are being identified in the very early stages of renal disease, before clinical signs are evident. This raised the question as to how we should manage these patients.

The ‘correct’ point at which to start a renal diet is a point of controversy: some argue that starting before signs of azotemia are seen may increase the chance of acceptance of the diet and have a ‘protective’ effect on the kidney. Others believe that the detrimental effects of protein restriction and high fat intake outweighs the possible benefits [11].

 

Conclusion

CKD remains one of the most common diagnoses in middle to older aged cats. The advent of SDMA test has advanced diagnosis of CKD and means that more cats are being identified early in the IRIS staging.

Dietary therapy for cats with CKD can have enormously beneficial effects, with cats on prescription diets living on average more than twice as long following their diagnosis than those on adult maintenance diets. Given the differing methodologies, countries, groups of researchers and diets being investigated in these 3 studies [4, 5, 7] the evidence strongly supports that feeding a renal diet to cats with CKD favours a better clinical outcome.

Royal Canin Veterinary Health Nutrition Renal diet is formulated to support renal function in cases of CKD. It has an adapted content of high-quality protein to reduce renal workload and prevent uremic crises. It contains omega 3 fatty acids EPA and DHA, a complex of antioxidants and a low phosphorus level. Formulated with alkalinising agents the diet helps maintain metabolic equilibrium and help prevent acidosis. It is highly palatable and readily accepted by patients.

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References:

1. O’Neill, D.G., et al., Longevity and mortality of cats attending primary care veterinary practices in England. J Feline Med Surg, 2015. 17(2): p. 125-33.
2. Marino, C.L., et al., Prevalence and classification of chronic kidney disease in cats randomly selected from four age groups and in cats recruited for degenerative joint disease studies. J Feline Med Surg, 2014. 16(6): p. 465-72.
3. Braff, J., et al., Relationship between serum symmetric dimethylarginine concentration and glomerular filtration rate in cats. J Vet Intern Med, 2014. 28(6): p. 1699-701.
4. Polzin, D.J. and J.A. Churchill, Controversies in Veterinary Nephrology: Renal Diets Are Indicated for Cats with International Renal Interest Society Chronic Kidney Disease Stages 2 to 4: The Pro View. Vet Clin North Am Small Anim Pract, 2016. 46(6): p. 1049-65.
5. Elliott, J., et al., Survival of cats with naturally occurring chronic renal failure: effect of dietary management. J Small Anim Pract, 2000. 41(6): p. 235-42.
6. Plantinga, E.A., et al., Retrospective study of the survival of cats with acquired chronic renal insufficiency offered different commercial diets. Vet Rec, 2005. 157(7): p. 185-7.
7. Ross, S.J., et al., Clinical evaluation of dietary modification for treatment of spontaneous chronic kidney disease in cats. J Am Vet Med Assoc, 2006. 229(6): p. 949-57.
8. Slatopolsky, E., The intact nephron hypothesis: the concept and its implications for phosphate management in CKD-related mineral and bone disorder. Kidney Int, 2011. 79121: p. S3-8.
9. Geddes, R.F., et al., Fibroblast growth factor 23 in feline chronic kidney disease. J Vet Intern Med, 2013. 27(2): p. 234-41.
10. Brown, S.A., et al., Beneficial effects of chronic administration of dietary omega-3 polyunsaturated fatty acids in dogs with renal insufficiency. J Lab Clin Med, 1998. 131(5): p. 447-55.
11. Scherk, M.A. and D.P. Laflamme, Controversies in Veterinary Nephrology: Renal Diets Are Indicated for Cats with International Renal Interest Society Chronic Kidney Disease Stages 2 to 4: The Con View. Vet Clin North Am Small Anim Pract, 2016. 46(6): p. 1067-94.

Postdate: 28th Jul 2020