Tanya's Comprehensive Guide to Feline Chronic Kidney Disease

This page explains more about the various functions of the kidneys.
It is because the kidneys have so many functions that there are so many possible symptoms of CKD. Which ones you might see depends upon which functions are affected.
This page also explains why CKD is so common in cats.
It discusses why CKD cannot normally be detected until two thirds of function has already been lost.

Main Functions of the Kidneys

The kidneys have five main functions:

the regulation of fluid levels in the body;

the regulation, including filtering and disposal, of waste products in the body;

the regulation of electrolytes (salts in the body's cells which are necessary for survival) in the body;

stimulation of red blood cell production; and

production of renin, which controls blood pressure .

In cats with CKD, as the kidneys become more and more damaged and their ability to function declines, an imbalance can arise in any or all of these areas. So, for example, a cat whose kidneys struggle with the production of red blood cells will develop anaemia.

Why CKD Occurs

Most cats develop CKD as a result of aging. Studies indicate that around 10% of cats over the age of ten will develop CKD. Older cats are at even greater risk: as many as 30% of cats over the age of 15 have the disease. Therefore, if you have a cat aged 15 or over, s/he has a one in three chance of developing CKD.

Younger cats may also develop CKD but it is less likely. If they are very young (less than two years old), this may be because of a congenital problem. Other possible causes include kidney infections, blockages or exposure to toxins.

The Cat Doctor mentions that CKD occurs twice as often in Siamese, Maine Coon, Abyssinian, Russian Blue and Burmese cats.

The Causes of CKD page explains more about the various possible causes, but in most cases the treatment will be the same whatever the cause.

The Role of Nephrons

The main work of the kidneys is performed by units called nephrons, which filter the blood flowing into the kidneys. The measure of the nephrons’ function is called glomerular filtration rate (GFR).

Khan Academy has a clear video showing how the nephrons work.

Why CKD Cannot Normally Be Detected at an Early Stage

A cat’s kidneys contain around 170,000 - 190,000 nephrons. This is actually many more nephrons than are needed for normal function; plus nephrons can increase their individual function to some extent when other nephrons die. This is why people can donate a kidney and still manage perfectly well with one kidney. In the case of a kidney transplant, if you remove one kidney from the donor, the donor's GFR (glomerular filtration rate, a measure of kidney function) will immediately fall to half of what it was, but will then gradually improve as the remaining nephrons increase their function to compensate for the loss of one kidney. Eventually the nephrons in the remaining kidney will reach almost the same level of function as two kidneys.

It works in a similar way in a cat with kidney disease, i.e. as damaged nephrons die (they are often described as "scar tissue"), other nephrons take over their work. Eventually, however, all the remaining nephrons will be working fulltime (i.e. there will be no "renal reserve" left). It is at this point, when around 66-75% of function has gone, that you will probably start to see symptoms in your cat, as the remaining nephrons start finding it harder to cope with the workload.

This is also why it is actually normal for CKD not to be diagnosed until at least 66% of function has been lost. So please do not feel guilty for not noticing sooner - there was probably nothing for you to notice, plus cats are very good at hiding signs of illness. CKD is not normally painful, so this makes it easier for the cat to hide what is happening. There are a number of possible methods of Early Detection, but some of these are quite specialised, and most people wouldn't know about them; in fact, not all vets are familiar with all of them.

Don't waste your energy beating yourself up. What you need to focus on is the fact that cats with CKD can often manage quite well on limited kidney function - for some cats, things only become critical when they have lost as much as 90% of function, and there are some cats who cope astonishingly well with even less function. So the goal is, not to worry about the function that has already been lost, but to try to retain the remaining function for as long as possible, and keep your cat feeling as well as possible. This site aims to help you with both goals.

Links to More Information

Long Beach Animal Hospital clearly explains more about the way the kidneys work.

The Merck Manual explains kidney function (with diagrams).

Feline Good describes how the kidneys work.

Cornell University College of Veterinary Medicine has a helpful video overview of feline kidney disease - click on Understanding Kidney Disease.

People and pets: common diseases - kidney disease is a video from University of California at Davis which provides an overview of what happens in CKD and shows a dog receiving dialysis. It also features a human CKD patient talking about how CKD feels.

Back to Page Index

This page last updated: 16 December 2010

Links on this page last checked: 16 December 2010