Chronic Renal Disease (CRD)

The information contained in this article is provided for general information only and is not intended to replace veterinary advice.

Please consult with your vet for further information.

 

 

The Kidneys & their Role

The kidneys are two small bean-shaped organs situated either side of the spinal cord, roughly in the middle of your cat’s back.

The kidneys are made up of hundreds of thousands of tiny filtering tubes called nephrons. The nephrons filter out the waste from the blood. The cleansed blood then goes back through the body, while the toxins and waste are excreted through the urine.

The kidneys do far more than simply filter waste though. They play a vital role in the health and well-being of your cat, affecting numerous important processes in the body:

• Excretion of waste: filtering out toxins, salts and urea
• Fluid level balances and blood volume: excreting fluid when too much has built up, retaining it in the case of dehydration
• Blood pressure regulation via 2 processes:
  • The Fluid balances mentioned above
  • The production of renin, an enzyme that causes the blood vessels to constrict and which also converts blood protein into a hormone called angiotensin which triggers production of another hormone, aldosterone, which helps control salt and water levels in the blood.
• Regulation of Blood pH by excreting hydrogen ions and secreting or reabsorbing bicarbonate
•  Red blood cell production through the production of the hormone Erythropoetin (EPO)
• Regulation of Vitamin D levels by converting calcidiol to calcitrol, the active form of Vitamin D. Calcitrol regulates the levels of calcium and phosphate in the blood, helping healthy bone growth, and also affects neuromuscular and immune function.
• Regulation of electrolyte and mineral levels

What is Chronic Renal Disease?

When chronic renale disease occurs, the nephrons – those tiny filtering tubes – start dying off over weeks and months – or even years, and are replaced with scar tissue. Normally, not all nephrons are used, so initially those not working step in to take over from the dead nephrons. As the disease continues, and more nephrons die, the remaining become bigger to try and make up for being fewer.

Eventually, however, they become overwhelmed, and are unable to handle and maintain usual kidney functions:

• Toxins and waste products start building up in the blood
• Thirst increases due to the toxins and waste, leading to increased urination. As a result, dehydration occurs and electrolytes and protein are flushed out, leading to weight loss and weakness
• Blood pH changes, leading to ulcers of the stomach and intestines and causing vomiting.
• Mouth and tongue ulcers may occur as bacteria in the mouth change uremic waste into ammonia. Gingivitis and Periodontal disease can worsen for the same reason.
• Hormone levels are disrupted leading to numerous problems:
  • The drop in EPO leads to anemia
  • Calcium can be deposited in the wrong places, leading to problems with the skeleton and internal organs
  • The Sodium imbalance leads to high blood pressure and all the problems surrounding that.
  • Phosphorous builds up: high levels can cause diarrhea, hardening of organs and soft tissues; the body’s ability to use many other minerals is affected and the phosphorous can combine with calcium to then form mineral deposits in muscles.

Symptoms of Chronic Renal Disease

CRD symptoms appear gradually, and are not specific to kidney disease, making them difficult to see and understand.
Not all symptoms will appear in all cats, and some will only be apparent in the latter or end stages of the disease:

•  Increased thirst & urination occurs in almost all cases and is often the first sign – but as these increase slowly over time they are not necessarily that noticeable
•  Weight loss
•  Poor appetite/anorexia
•  General weakness and lack of energy
•  Vomiting & diarrhea
•  Bad breath or breath that smells of ammonia
•  Mouth/tongue ulcers
• Gingivitis & periodontal disease
• Itchy skin may occur from calcium & phosphorous deposits
• Bleeding in the stomach may occur due to stomach/intestinal ulcers – seen in the form of blood in the stool (either black tarry stool or simply blood seen)
• Blindness may occur in the later stages (linked to high blood pressure)
• In the end stages, seizures and coma

 

Causes of Chronic Renal Disease

Causes of CRD, and the reasons for the high incidence in cats, are not very clear in most cases. Factors that may contribute include:

• The breed – certain breeds seem predisposed to CRD: Siamese, Persian, Abyssinian, Burmese, Maine Coon and Russian Blue
• Hereditary/Congenital diseases:
  • Polycystic Kidney Disease : cysts form on the kidneys
  • Renal Dyplasia or Renal Hypoplasia: the kidneys either do not form normally or do not form completely
  • Reflux Nephropathy: the kidneys are damaged by urine flowing backwards into the kidneys – a genetic form exists in Ragdolls
• Infections
• Dental problems
• Hypertension – caused by but also a possible cause of CRD
• Kidney stones and obstructions
• Toxins – often the result is Acute Kidney Disease, but residual and long lasting damage may occur, leading to CRD
• NSAIDs (non-steroid anti-inflammatory drugs)
• Diet:
  • Feeding dry food causes dehydration, as cats do not drink enough to make up for the lack of moisture: the dehydration may be a contributing factor by allowing less fluid to irrigate the kidneys
  • Many commercial diets are “acified” to prevent the formation of struvite crystals. As a consequence though, the urine can become too acid, causing the formation of calcium oxalate stones – which are a risk factor for CRD

 

For information on Diagnosis, Food, Treatments & Additional links please see the following pages.

 

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