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“Elderly cat, drinking a lot, losing weight’ – a common reason for an appointment on the diary. One of the most common causes – though by no means the only one – is kidney disease. Chronic kidney disease is very common in older cats. But why? And what can we do about it?

The kidneys are organs of excretion – they primarily exist to process waste. However, they are also responsible for the fluid and salt balance of the body, the production of certain hormones, and are important in controlling blood pressure. We unfortunately don’t yet understand the cause behind most cases of chronic kidney disease (CKD). Although some cases have known causes – such as the genetic condition polycystic kidney disease, or exposure to certain toxins – in most cases all we really know is that chronic inflammatory changes lead to a gradual loss of kidney function. Chronic kidney disease is about three times as common in cats as it is in dogs; it is estimated that between 20% and 50% of cats over 15 years old will have some degree of CKD.

What are the signs of CKD?

In the early stages, there are actually no obvious clinical signs of CKD. This is because the kidneys have a great reserve capacity (which is why humans can donate a kidney and lead a healthy existence with just one). Clinical signs of chronic kidney disease are not seen until between two thirds and three quarters of functional kidney tissue has been lost.

Common signs of kidney disease are:

• Increased urination. The kidneys are no longer able to concentrate urine and retain fluid within the body, so a large volume of dilute urine is produced. This leads to…
• Increased thirst – as the body tries to compensate for fluid loss. However, the body is not able to retain enough fluid to keep up with losses. Cats with CKD tend to suffer from…
• Dehydration. Signs of dehydration include sunken eyes, tacky mucous membranes in the mouth, and loss of skin elasticity, so when skin is tented up it is slow to lie flat again.
• Weight loss. Cats with kidney disease often do not eat well, so lose weight. Poor appetite is often due to…
• Nausea. High levels of waste products that the kidney normally filters out (such as urea) can lead to nausea and poor appetite.
• Halitosis. High levels of urea in the blood produce a distinctive unpleasant smell to the breath.
• High blood pressure – this does not come with external signs, but cats that are suffering from CKD will often have elevated blood pressure. This can lead to consequences such as retinal haemorrhage or retinal detachment, both of which can lead to blindness.
• Anaemia. The kidney produces the hormone erythropoietin, which tells the bone marrow to produce new red blood cells. Loss of kidney function also leads failure of erythropoietin production, so as red blood cells reach the end of their lifespan, they are not replaced with new red cells, and so anaemia gradually develops.

What can we do about it?

Unfortunately, there is currently no cure for chronic kidney disease. Once kidney tissue has been damaged, there is no way for it to regenerate. Treatment therefore focuses on slowing the rate of progression, and ensuring that the cat maintains a good quality of life.

Renal diet – Feeding a cat with chronic kidney disease correctly is very important, and there are several veterinary diets available to support a cat with CKD. The main feature of these diets is that they have a restricted protein content. The breakdown of excessive protein in the diet produces urea, which the kidney is then not able to effectively filter. High levels of urea in the blood make the cat feel unwell. However, the food needs to have enough protein and calories to maintain the cat’s body weight and muscle mass. Renal diets are also restricted in phosphorus, which tends to accumulate in the blood of cats with kidney disease. High levels of phosphorus can lead to further damage to the kidneys. As cats prefer to obtain the majority of their water requirements from eating, rather than drinking, it is advised that cats with kidney disease are fed wet food. This helps meet their increased requirements. However, biscuit diets are available for cats that prefer to eat biscuits.

Feeding a renal diet to a cat with CKD has been proven to significantly extend their life expectancy. The best time to consider a diet switch if at all possible is before the cat starts to feel unwell. This is one reason why monitoring older cats closely for signs of CKD is recommended.

• Managing high blood pressure – Hypertension is common in cats with kidney disease. High blood pressure can further damage the kidneys. There is also a risk of serious consequences such as blindness. High blood pressure in cats is most commonly managed with a medication call amlodipine.
• Treating proteinuria – In some forms of kidney disease, protein is lost in the urine. Presence of large protein molecules in the tubules of the nephron (a part of the kidney where they should not normally be found) can lead to worsening kidney disease, so controlling this is important. This is achieved using drugs known as ACE inhibitors or angiotensin receptor blockers (ARBs).
• Managing nausea and gastritis – In the later stages of CKD, cats may show signs of nausea and be unwilling to eat. Their quality of life can be improved by using antacid medication, or periodically treating with anti-emetic medication, as long as they are otherwise well and their condition is well-managed.

Early detection of CKD

There is a misconception that, because a condition is incurable, there is nothing we can do to help a patient suffering from that condition. Owners will often notice changes such as weight loss or increased drinking, but may delay bringing the cat in. They might feel the cat is otherwise still well, or consider these changes to be a ‘normal’ part of ageing. Sometimes pet owners may even think that the only thing we can advise is euthanasia. However, with better understanding of the disease, and new, easier-to-give medications becoming available all the time, there are now a lot of things we can do to support cats with chronic health conditions.

If we diagnose CKD in a cat that is already very unwell, it can be extremely difficult to manage. They are often very dehydrated and require hospitalisation and intravenous fluid therapy to correct this. Starting treatment at this stage can be challenging. This particularly applies to a dietary change; cats in this condition are often feeling unwell, and offering them a new food at this point can lead to a learned taste aversion.

For this reason, we recommend monitoring older cats carefully for signs of ill-health, including CKD. The International Society of Feline Medicine recommends a yearly health check for all cats, and twice yearly for older cats. Regular measurement of body weight, and regular testing of urine is recommended; changes in these might be early signs of kidney disease, and will likely be detected much earlier than changes in appetite or drinking.

One easy, cost-effective way to manage this is to book your cat in for a Senior Cat Health Check. This special extended consultation with a vet and a nurse includes a full health check, body weight check, blood pressure measurement and urine test. Normally these procedures, booked separately would cost over £100; however a senior clinic costs only £50 – a saving of over 50%.

Early detection of CKD means a better response to treatment, better on-going quality of life and ultimately a longer life expectancy for your well-loved family member.

Dr Lucy Fleming MRCVS