The basics about the kidneys
So let’s get started by talking a little bit about what the kidneys are and what they do. Like humans, dogs and cats have two kidneys which lie in the abdominal or belly area, one on the left side and the other on the right side. The kidneys are essential for maintaining water and salt balance in the body. They receive a lot of blood which they filter to take out a variety of waste substances that need to be removed from the body. These substances include for example urea, creatinine, potassium and acid, all of which if they accumulate in the body can cause severe and in some cases life-threatening problems. The kidneys also remove or hold onto water as necessary to keep the body hydrated. They produce urine which then flows down to the bladder where it is stored and intermittently excreted by the animal from the body. The process of urine production occurs continuously in a healthy animal.
- The first is where enough of the units are damaged and the function of the kidneys becomes so severely reduced that the animal develops what we call acute kidney injury and failure. When the units in the kidney are damaged, they can recover if the damage is not too severe so some of these animals with acute kidney injury can go on to recover. However if the units are damaged too severely, they essentially die off and the failure is irreversible as new units cannot be formed.
- The second scenario is where the kidney suffers an injury that is not too bad at the outset; you may not notice anything different about your pet. However this sets of a process whereby the units in the kidney slowly die off until eventually, after months or even years, enough of them are lost and your pet starts to show signs of being unwell. We refer to this as chronic kidney failure. In some of these animals, you will notice relatively mild signs of illness that will nevertheless prompt you to see your vet.
- However in a small number, your pet which seemed to be doing ok suddenly deteriorates very quickly. In this our third scenario, the animal has what we refer to as an acute decompensation or crisis of their chronic kidney failure.
- Drugs are one possible cause. Some of the drugs that are used very commonly in dogs and cats can injure the kidneys, either if too much is given or if they are used in the wrong circumstances. Non-steroidal anti-inflammatory drugs, or NSAIDs, such as carprofen or meloxicam, are one group of drugs that are known to potentially injure the kidneys. It is important to realise that we are not saying that animals should not receive these drugs, just that we need to be aware of their potential to injure the kidneys if used at doses that are too high or under the wrong circumstances.
- Toxins or poisons are something else that can injure the kidneys and cause kidney failure and these animals often go from being completely healthy to quickly developing acute kidney failure that makes them very sick. Examples of poisons that can do this include ethylene glycol which is contained in anti-freeze, as well as grapes, raisins, currants or sultanas in dogs, and lily plants in cats. We discussed these poisons in episodes 2 and 3 of these blogs so please have a read of those if you haven’t already.
- Infections are another potential cause of kidney disease. In particular dogs can be affected by a bacterial infection known as leptospirosis. There are a number of different strains of this bacterium but many of them cause kidney injury. In particular the strain that is most common in the United Kingdom as well as in other parts of the world tends to cause kidney injury as well as damage to the liver so the patient develops both kidney failure and jaundice. We also see so-called pyelonephritis in dogs and cats where a bacterial infection affects the kidneys only and can cause their function to be compromised.
- Cancer is another potential cause of kidney disease that we see. In particular a type of malignant cancer known as lymphoma can affect the kidneys as well as many other sites in the body.
- And certain breeds of cat, such as Persians or Exotic short hairs, can be affected by a condition known as polycystic kidney disease (PKD) in which cysts form in the kidneys. PKD is an inherited condition and can take a long period to become a problem clinically.