Kidney Function & Clinical Symptoms

Clinical symptoms of CKD

The clinical symptoms of CKD are as diverse and numerous as the functions of the kidney. In addition, each cat has its own individual kidney-related vulnerability. That means that every cat presents a different pattern of symptoms and not every symptom occurs in every cat.

Mostly, the symptoms appear gradually over weeks, months and years and are often only noticed when 2/3 to 3/4 of the nephrons have already been destroyed.

Many of the known symptoms have several causes. And some clinical symptoms are also interrelated. For example, nausea leads to an aversion to eating, which in turn leads to emaciation and, ultimately, bodily weakness. Weakness, in turn, can cause a cat to become “wobbly” on its legs, which is also apparent in the hind limbs (hind-limb weakness).

Vomiting can exacerbate dehydration. Inflammation of oral mucous membranes and peptic ulcers can lead to malnutrition and nausea.

Anorexia, apathy, lethargy, weakness and weight loss as well as increased drinking (polydipsia) and excessive urine production (polyuria) are the main symptoms of chronic kidney disease (CKD).

Most symptoms are easily treated. Reducing their causes, in particular, is effective in alleviating clinical symptoms. It constitutes an important part of treatment.

Water and electrolyte balance

The kidneys regulate water and electrolyte/mineral loss and thus balance the volume of water in the body. Excess electrolytes (for instance potassium, calcium and phosphate) and excess water are eliminated.

If less water is drunk, water and electrolytes can also be retained by decreasing urine production. Since over 75% of the body consists of water, and even a 2% reduction in body fluid is dangerous, it is clear how finely tuned the role of the kidneys is in regulating and maintaining fluid and electrolyte balance.

Regulation of water balance

Loss of the ability to reabsorb water and loss of regulation of salt and other electrolytes in the body.

  • Increased drinking (polydipsia)
  • Increased urine production (polyuria)
  • Dehydration → until collapse
  • Increased drinking (polydipsia)
  • Increased urine production (polyuria)
  • Dehydration → until collapse

Regulation of electrolyte balance

Loss of fine regulation of the electrolyte balance can lead to secondary hyperparathyroidism

  • Lack of appetite (anorexia)
  • Fatigue (apathy), weakness, lethargy
  • Weight loss
  • Itchiness
  • Twitching
  • Teeth grinding
  • Impaired movement (for example weakness of the hind legs) and abnormal movements like walking on hocks (plantigrade gait), uncoordinated movements
  • Constipation
  • Eating cat litter
  • Hypothermia

Regulation of blood pressure

The kidneys also influence blood pressure via control of water and electrolytes. The kidneys actively regulate this by producing a hormone known as renin.

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Regulation of pH

The kidneys can eliminate both increased acids and bases, as required, and thus regulate the pH of the blood, which is essential for metabolic activity. Many enzymes are dependent on the pH of the blood to function correctly.

The loss of fine regulation of pH in the body can lead to increased acidity of the blood (metabolic acidosis)

  • Weight loss and muscle atrophy
  • → Spine becomes visible and bony
  • Shortness of breath, increased panting
  • Mucosal ulcers in the mouth (stomatitis)
  • Vomiting

Production of hormonal substances

Erythropoietin is an essential hormone for regulating red blood cell (erythrocyte) production. Renin controls blood pressure. Calcitriol is the active form of vitamin D and regulates calcium and, thus, secondarily also phosphate levels in the blood. If there is too little calcium in the blood, calcitriol is released to reduce calcium excretion. In addition, if there is too little calcium in the blood, parathyroid hormone is released from the parathyroid glands, which liberates phosphate and calcium from the bone through bone resorption. Excess parathyroid hormone levels can lead to softening of the bones. Thus, the kidneys indirectly influence bone metabolism via regulation of calcium and phosphate excretion.

Reduced calcitriol production (vitamin D)

A decrease in calcitriol production can lead to secondary hyperparathyroidism.

Disruption of renin synthesis

Disruption of renin synthesis can be associated with high blood pressure.

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  • Central nervous disorders such as seizures, convulsions, lethargy, stroke
  • Walking difficulties
  • Central nervous disorders such as seizures, convulsions, lethargy, stroke
  • Walking difficulties

Reduction in erythropoietin synthesis

Disruption of erythropoietin synthesis can lead to anaemia

  • Fatigue (apathy), weakness, lethargy → hind leg weakness
  • Lethargy
  • Paleness of the mucous membrane of eyes, ears and mouth
  • Hypothermia, cat cold to the touch, feels cold, shivers
  • Nausea, lack of appetite (anorexia), eats cat litter
  • Increased heart and breathing rate

Removal of toxins

The kidneys continuously filter metabolic waste products and foreign substances (for instance drugs) from the blood and excrete them in the urine. Urinal substances of this kind include those that no longer have a function in the body and also toxins and toxic metabolic products, for instance from protein metabolism. These uraemic toxins can accumulate in the blood if less urine is passed and then directly damage the kidneys, blood vessels and impair bone metabolism.

  • Diarrhoea → emaciation, dehydration
  • Shaggy coat
  • Fatigue (apathy)
  • Stomach ulcers which can lead to bleeding
  • Tremor, cramps, abnormal movements, muscle disorders, comatose states