Where are the kidneys and how do they work? Dogs, like all mammals, have two kidneys that are located just below their spinal column (Fig 1) at the angle between the ribs and the softer body wall.
Fig 1: abdominal X-ray showing the position of the kidneys
The kidneys have a number of important functions including:
removing waste material from the body via the urine
water balance
managing the amount of sodium, potassium, phosphorus and calcium in the blood
Beyond this the kidneys are also responsible for a number of other activities such as:
stimulating the bone marrow to produce red blood cells
activating vitamin D
The kidneys are made up of millions of little filtration units called ‘nephrons’ that are each comprised of a filter (called a ‘glomerulus’, which works like a sieve) and a long tube that modifies the material that has been filtered to produce urine. All these little tubes are collected together at the centre of the kidney and empty into a small tube (the ‘ureter’) that carries the urine to the bladder for storage (Fig 2). Over time, with age and wear and tear, individual nephrons stop functioning and die; this is not normally a problem as there is an enormous amount of spare capacity (that’s why we can donate a kidney). In some individuals, however, disease causes a more rapid loss of nephrons over a prolonged period of time to the point that there aren’t enough nephrons left to perform all the kidneys’ necessary functions. This is called ‘chronic kidney disease’ (CKD).
Fig 2: relationship of kidney (K), ureters (u), bladder (B) and urethra (UR)
What are the signs of chronic kidney disease? Signs of chronic kidney disease are slowly progressive and are usually first seen as an increase in urination and thirst – sometimes this is seen as a dog starting to have accidents in the house if left for longer periods. As kidney disease becomes more advanced, other signs may become evident such as weight loss and reduced appetite, vomiting, diarrhoea, smelly breath, reduced ability to exercise and poor coat quality.
How is chronic kidney disease diagnosed? The diagnosis of chronic kidney disease, other than in the very early stages, is usually relatively straightforward, involving blood and urine tests and often blood pressure measurement. In some cases, other investigations may be appropriate such as ultrasound to try and establish whether there is a treatable underlying cause such as stones. A variety of blood and urine parameters are measured to confirm that the changes are due to kidney disease and not some other disease process. Most commonly your vet will talk to you about the levels of urea and creatinine, as these are some of the waste products excreted by the kidneys; as kidney function declines, their levels increase. There is a 4 stage classification system based on the level of creatinine as a benchmark for the severity of chronic kidney disease. As the kidney has many functions, and to help your vet decide on the best treatment, a number of other blood and urine values can be important such as albumin, potassium, sodium, calcium and phosphorus, the concentration of the urine, the amount of protein in the urine and whether infection is present. Some dogs with chronic kidney disease will become hypertensive (high blood pressure), so blood pressure measurement may be necessary.
How is kidney disease treated? Unfortunately most kidney disease is due to a chronic ‘glomerulonephritis’ (damage to the tiny filters – called ‘glomeruli’ – inside the kidneys) which, by the time of presentation, is not directly treatable. There are, however, a variety of ways that the kidneys can be supported. Management is aimed at slowing the progression of the disease as far as possible. Key areas of management are:
It’s important that dogs with chronic kidney disease have access to plenty of water
Ensuring adequate fluid intake – it is essential to realise that it is the dog’s inability to concentrate its urine that leads to increased urination and that in order to maintain hydration the dog needs to drink more i.e. it is the urination that is driving the drinking and not the other way around. For this reason it is vital that water intake is not restricted, even if the dog is having accidents; it also means that if your dog becomes ill for any reason and stops drinking normally they will become dehydrated more quickly.
Controlling blood phosphorus levels – high blood phosphorus has been shown to result in more rapid progression of kidney disease. In many dogs, phosphorus levels can be controlled with diet, but in some cases additional support needs to be given and your vet may prescribe oral phosphate binders. Low dose vitamin D therapy is indicated in some circumstances. Controlling urine protein loss – increased protein in the urine is also associated with progression of kidney disease. Excess protein loss is usually treated with an angiotensin converting enzyme (ACE) inhibitor. Controlling blood pressure – high blood pressure further damages the nephrons, so keeping blood pressure within the reference range is important; medication is usually required to achieve this. Other treatments – a variety of other treatments may be prescribed by your vet, such as omega-3 polyunsaturated fatty acids, potassium citrate or potassium gluconate, antacids and anti-nausea drugs. In some circumstances, more advanced kidney disease requires additional treatments to be considered such as erythropoietin therapy or tube feeding.
Some drugs routinely used in veterinary medicine can be a problem for dogs with chronic kidney disease so it is worthwhile reminding your vet if you are taking your dog to see them for another reason that they also have kidney disease.
Will monitoring of kidney function be required? There are a number of options for managing chronic kidney disease in dogs
Ideally, regular blood and urine tests will help to ensure that the management of your dog’s chronic kidney disease is optimal. The frequency of these tests will depend on the stage of kidney disease and the rate that the disease appears to be progressing.
What about kidney transplantation? Kidney transplantations for animals are not available in the UK and experience from elsewhere in the world has found that it is a complicated procedure with significant post-operative problems. The survival time following transplantation is relatively poor and does not seem to give any real advantage over good management of chronic kidney disease.
What will happen in the end? In the vast majority of cases, chronic kidney disease is progressive, so ultimately there will not be enough kidney function to support life. BUT with early diagnosis and good management it can take years to reach this point and your dog can continue to enjoy a good quality of life.
About Kit Sturgess
Kit is a Royal College of Veterinary Surgeons recognised specialist in internal medicine and has been in clinical practice for over 25 years. He now provides independent specialist internal medicine services to colleagues in general practice. Kit has authored two textbooks and lectures internationally.
The Veterinary Expert| Pet Health
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