What causes kidney failure in cats?

Kidney disease is one of the most common degenerative conditions in cats, especially in the elderly. However, it can also occur in younger animals exposed to certain toxins or infections. In this blog, we’re going to have a brief look at the more common causes of kidney failure in cats, and the symptoms that they cause.

What are the functions of the kidneys?

The main function of the kidneys is to filter the blood, removing waste materials (like potassium, urea, creatinine, certain drugs, and excess water and salts) but keeping what the cat needs (like proteins, glucose, sodium and enough water to maintain their hydration).

They also produce certain hormones, especially renin (which helps to regulate blood pressure) and erythropoietin (which controls the production of red blood cells).

What are the symptoms of kidney disease?

There are two different types of kidney disease, with subtly different symptoms. In either case, however, there will be no symptoms until more than 75% of the kidney tissue (i.e. one and a half kidneys!) have been lost – this is the “functional reserve capacity” of the renal system.

Acute Kidney Injury

This occurs when the kidneys are suddenly injured, e.g. by a toxin, or a sudden dangerous drop in blood pressure. Typical symptoms are sudden in onset, and include:

  • Loss of appetite.
  • Lethargy or even collapse.
  • Vomiting and (sometimes) diarrhoea, possibly with blood.
  • Altered urination – increased in mild cases, reduced or even absent in the most severe ones.
  • A metallic smell on the breath.
  • Seizures, coma and death.

Chronic Kidney Disease

This happens when the damage is more gradual, and the symptoms tend also to appear more gradually and may be subtle and non-specific:

  • Loss of weight
  • Weak, but not usually absent, appetite
  • Tiredness and lethargy
  • Occasionally vomiting.
  • Increased thirst
  • Increased urination
  • Poor coat quality (often a “staring” coat)
  • Anaemia, as the damaged kidneys do not produce enough erythropoietin.
  • Metallic breath, but not usually as dramatic as in acute conditions.
  • Muscle weakness, due to the loss of potassium salts.
  • High blood pressure, caused by overproduction of renin, that may cause strokes or blindness.

What can cause kidney failure?

There are a wide range of possible causes; in some cases, two or more will interact to cause more severe kidney damage than would normally be expected. Common causes include:

  • Infection of the kidney (pyelonephritis). This may occur with bacteria that spread up from the urinary tract, or through infections carried in the blood (e.g. from dental disease).
  • Oxygen starvation, usually caused either by shock (e.g. after a road traffic accident) or low blood pressure (e.g. in an anaesthetic – this is why we like to monitor blood pressure so carefully during surgery!). The kidney cells are metabolically very active and need a constant supply of oxygen – if this is interrupted, then cells start to die.
  • Certain systemic viral infections (especially feline leukemia virus (FeLV), feline immunodeficiency virus (FIV), and feline infectious peritonitis (FIP)).
  • Polycystic Kidney Disease (PKD) – this is a genetic disease, most commonly seen in Persian cats, where fluid-filled cysts form in the kidneys and crush out the normal, healthy tissue, resulting in early onset chronic kidney failure.
  • Poisonings – especially with antifreeze, or as a side effect of certain painkillers, although this is rare. These usually cause acute kidney injury, although they may contribute to chronic disease later in life.
  • Kidney tumours, especially a cancer called lymphoma which can form within the kidney tissues.
  • Blocked bladder – where a stone prevents the cat from urinating. The bladder fills with urine, and the back-pressure then damages the kidneys. If not treated, however, the bladder will rupture and the cat will soon die of internal poisoning.
  • “Wear and tear” – unfortunately, simple old age takes its toll on how efficient the kidneys are! Because cats are obligate carnivores (i.e. they have to eat meat to survive), they need a high protein diet. The more protein there is in the diet, the harder the kidneys have to work to filter the blood – and so the earlier signs of kidney problems are likely to turn up. This is probably why cats have a higher risk of kidney disease than dogs, who are omnivores with a lower protein requirement.

How can kidney disease be treated?

Some very mild acute kidney injuries which, if treated immediately, may be partially reversible. However, in general, kidney disease cannot be cured. It can, however, be managed, with medication, a suitable renal diet, and careful monitoring (of kidney function and blood pressure, among other parameters).

If you think your cat may have kidney disease, contact one of our vets for advice.