Kidney Disease in Dogs

Kidney disease may occur in dogs of all ages and can develop as either an acute or chronic condition. Although the symptoms are generally similar, the long-term prognosis can vary greatly depending on the underlying cause. This article offers an overview of the symptoms, causes and treatment of canine kidney disease.

A quick look at normal kidney function

The kidneys are paired organs located in the abdominal cavity that serve several essential regulatory roles. They filter the blood to remove wastes such as urea and ammonia, which pass via tubes called ureters to the urinary bladder and are subsequently excreted. The kidneys produce several important hormones such as erythropoietin, which is responsible for red blood cell production. In addition, they regulate blood pressure by maintaining salt and water levels and are responsible for electrolyte and acid-base balance. The kidneys are composed of numerous structures called nephrons, each of which functions to filter waste and produce urine. They control how concentrated the urine is. When kidney disease occurs, these normal functions may be impaired, resulting in some of the symptoms displayed.

Kidney disease terminology explained

The terminology for kidney disease can be quite confusing. You may hear the word 'renal' - this is simply an adjective meaning 'kidney'. 'Renal disease' merely implies the existence of lesions within the kidneys, whereas 'renal failure' is a state of decreased kidney function. Renal failure occurs after approximately three-quarters of the nephrons of both kidneys have ceased to function. When this occurs, the kidneys are no longer able to produce concentrated urine and there is a build-up of nitrogen-containing waste products in the blood (the latter is known as 'azotaemia').Chronic renal disease is the most common disorder of the kidneys in dogs, and is defined as 'the presence of functional or structural abnormalities of one or both kidneys'. There is an irreversible loss of functioning nephrons, leading to decreased kidney function. By definition, for a dog to have chronic kidney disease, kidney damage or reduced kidney function must have been present for at least 3 months.Acute renal disease occurs when there is a sudden attack on the kidneys. In practice, the damage is normally so severe that acute renal failure occurs.

What are the symptoms of kidney disease?

Dogs with chronic kidney disease commonly show symptoms which get progressively worse over the course of several weeks or even months. These may include:

• Increased drinking
• Increased urination (sometimes with 'accidents' in the house or car)
• Decreased appetite
• Vomiting
• Weight loss
• Lethargy
• Bad breath

Because of the nature of acute renal failure, symptoms come on very suddenly and tend to be very severe. Many of the symptoms are the same as those above, but more marked. Other signs include, but are not limited to:

• Weakness/collapse
• Depression
• Abdominal pain
• Change in mental state/disorientation
• Seizures
• Pale gums and other mucous membranes (from anaemia)
• Blindness (as a result of high blood pressure)

What are the causes of kidney disease?

1. Chronic renal disease:There are many potential initiating causes and it is often difficult to identify the factor (s) responsible. Causes include:

• Inherited kidney conditions (most common in purebred dogs)
• Infections
• Toxins
• Immune conditions
• Kidney tumours
• Obstruction to urine outflow

2. Acute renal failure:This can occur due to:

• Loss of/lowered blood supply to the kidneys e.g. dehydration, prolonged/bad reaction to a general anaesthetic
• Toxins e.g. accidental ingestion of poisons

How are kidney disorders diagnosed?

Your vet will be able to gain a suspicion of kidney disease from taking a history and performing a physical examination of your dog. He/she will then need to perform blood and urine tests to confirm the diagnosis of kidney disease and rule out other causes of the symptoms. These can often give a clue as to the severity of the problem. Blood pressure is normally checked as abnormalities may be a cause or effect of kidney disease. Other tests such as abdominal x-rays or ultrasound of the kidneys may be indicated, depending on the suspected underlying cause (s) and whether your budget allows these. A kidney biopsy is sometimes performed but this procedure carries a small degree of risk.

How are kidney disorders treated?

Treatment will depend on the severity of the condition, its underlying cause and whether it is acute or chronic.Chronic kidney disease is generally not reversible but can be managed in order to reduce the symptoms and slow down the progression to complete kidney failure. If an underlying cause is identified then ideally this should be treated where possible e.g. antibiotic therapy in cases caused by bacterial infection. Restriction of dietary phosphorous, and supplementation with omega-3 fatty acids (e.g. from fish oils) are beneficial to dogs with chronic kidney disease. Specialised canine 'kidney' diets are available to meet these requirements. Medications called ACE inhibitors help to improve blood flow to the kidneys and prevent high blood pressure from occurring as a consequence of the disease. If your dog is quite poorly when diagnosed then a few days of intravenous fluid therapy and symptomatic treatment for nausea/vomiting may help. Dogs with acute renal failure can sometimes be managed supportively whilst the kidneys are given time to try to regenerate; however, both short- and long-term outlook depend on the underlying cause and severity of damage and this is best discussed with your vet on an individual case basis. On the whole the prognosis is fairly guarded. Typically treatment starts with aggressive intravenous fluid therapy over the course of several days or even weeks. These patients need close monitoring as abnormalities in electrolyte and/or acid-base balance often occur which may be life-threatening. Any vomiting or loss of appetite should be managed. Your vet will need to take regular blood samples to determine how your dog is responding to treatment, but your pet's demeanour and appetite are also good indicators. If he/she appears to be responding well then treatment can be slowly tapered and ultimately withdrawn, but on-going monitoring is advisable.

How do I prevent my dog from getting kidney disease?

Kidney disease in dogs is often just 'one of those things', whereby no one has done anything wrong and there's nothing you could have done to prevent it. However, here are a few pointers to reduce the risk to your dog:

• Grapes and raisins can cause acute renal failure in dogs - don't let your pet have access.
• Likewise, antifreeze (ethylene glycol) can also cause acute renal failure - it tastes sweet so can be tempting to the unsuspecting dog.
• Keep your dog up-to-date with vaccinations - leptospirosis can cause kidney disease/failure.

Not prevention, strictly speaking, but the following can also help:

• Take older dogs for a check-up with the vet at least annually (ideally every 6 months). A simple blood and urine test can pick up kidney disease in its early stages and many vets now offer special 'geriatric' screening tests.
• Measure your dog's water intake every month. If it starts increasing, this could be a sign of kidney disease or another disorder, and a vet check is advised. Normal water intake is usually less than 60ml per kg of bodyweight per 24 hour period, and should not exceed 100ml/kg/24 hours. Remember that if you change your dog from a wet to a dry diet, or if it is hot, he/she will drink more!
• Of course, monitor your dog closely for any of the symptoms listed above and take him/her for a check-up if you are concerned.