explains more about the various functions of the kidneys.
because the kidneys have so many functions that there are so many
possible symptoms of CKD. The symptoms you might see depend upon which
functions are affected.
This page also explains why CKD is so common in cats, and why CKD cannot normally be detected until two thirds of
function has already been lost.
Main Functions of
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) and minerals in the body
stimulation of red blood cell production
of renin, which controls blood pressure
In cats with
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
How the Kidneys Work
in order to understand what happens in CKD,
it helps to have a rough idea of how the kidneys work.
The main work of the kidneys is performed by units
called nephrons. The nephrons filter the blood flowing into the kidneys
via their glomeruli (see below). Healthy cats have about 170,000 -
190,000 nephrons, far more than they need, which is known as the renal
There are a
number of different causes of kidney disease.
Management and treatment of chronic kidney disease
in cats (2016)
Caney S In PracticeOct 2016 pp10-13 states "CKD is
the end result of a wide range of primary disorders that cause
irreversible damage to nephrons, eventually leading to reduced glomerular
filtration rate (GFR)."
is the most commonly seen type of kidney problem in cats, so when a vet says a cat
has CKD, s/he often means chronic interstitial nephritis.
interstitial nephritis is not a disease as such.
Renal fibrosis in feline chronic kidney disease:
known mediators and mechanisms of injury
(2015) Lawson J, Elliott J, Wheeler-Jones C, Syme H & Jepson R
The Veterinary Journal 203(1) pp 18-26 says "In most cases the
underlying aetiology is unknown, but the most frequently reported
pathological diagnosis is renal tubulointerstitial fibrosis. Renal
fibrosis, characterised by extensive accumulation of extra-cellular matrix
within the interstitium, is thought to be the final common pathway for all
kidney diseases and is the pathological lesion best correlated with
function in both humans and cats."
Renal diseases in cats
(2015) DiBartola SP Presentation to the Idexx Finland Congress
says "Chronic interstitial nephritis is a common morphologic diagnosis and may
represent the end result of
several different renal diseases including chronic glomerulonephritis and
chronic pyelonephritis. In most
patients, however, the inciting cause of the progressive renal disease
cannot be determined."
If you're not a
vet, you are
probably none the wiser after reading the above. Essentially, whatever the
initial cause of the CKD, inflammation and fibrosis (the formation of
excess fibrous connective tissue) occur and the end result is a cycle of
Cats with chronic interstitial nephritis have small, shrivelled kidneys
with scar tissue, and this is what is seen in most CKD cats.
Feline chronic kidney disease
(2015) Grauer GF Today's Veterinary Practice5(2)
pp36-41 says "the end point of irreversible glomerular or tubular damage is the same:
fibrous scar tissue replacement of nephrons."
There are a
number of reasons why CKD occurs in cats, see Causes of CKD
and immediately above. However, in most cases there is little you could
have done to prevent it because one of the main factors in the development
of CKD in cats is aging. Studies indicate that around 10% of
cats over the age of ten will develop CKD. Older cats are at even greater
risk: Chronic Renal Disease in Cats (1989)
Current Veterinary Therapy X, Krawiec DR &
Gelberg HB, Ed. Kirk RW, WB Saunders Company p. 1170-1173 found that 30%
of cats over the age of 15 had the disease.
A more recent study,
Disease surveillance and referral bias in the
veterinary medical database (2010)
Bartlett PC, Van Buren JW, Neterer M & Zhou
C Preventive Veterinary Medicine94(3-4) pp264–271, found that 28% of
the cats over the age of 12 who were examined at four US veterinary
hospitals had CKD. Therefore, if you have a cat aged 12-15 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), they may have a congenital
problem. Other possible causes include kidney infections, blockages or
exposure to toxins (though cats with these problems may have
The Cat Doctor
mentions that CKD occurs twice as often in Siamese, Maine Coon,
Abyssinian, Russian Blue and Burmese cats.
Cannot Normally Be Detected at an Early Stage
I often hear
from people who are kicking themselves for not realising sooner that their
cat was sick.
is actually normal for CKD not to be diagnosed until
as much as 66% of function has been lost, if not
The 170,000 - 190,000
nephrons found in a cat's kidneys are 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
filtration rate (GFR, 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,
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
Feline chronic kidney disease
(2015) Grauer GF Today's Veterinary Practice5(2)
pp36-41 states "Progressive diseases that slowly destroy nephrons allow
intact nephrons to undergo compensatory hypertrophy, which can delay onset
of renal failure. Therefore, when renal failure occurs (< 25% of the
original nephrons functional), nephron hypertrophy can no longer maintain
adequate renal function."
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
are a number of possible methods of
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, although there is a new test (introduced in 2015) called the
This is a simple blood test available through IDEXX Laboratories which may
help detect CKD sooner, but even then it can only detect CKD when 40% of
function has gone.
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
TREATING YOUR CAT WITHOUT VETERINARY ADVICE CAN BE
tried very hard to ensure that the information provided in this website is
accurate, but I am NOT a vet, just an ordinary person who has lived
through CKD with three cats. This website is for educational purposes
only, and is not intended to be used to diagnose or treat any cat. Before
trying any of the treatments described herein, you MUST consult a
qualified veterinarian and obtain professional advice on the correct
regimen for your cat and his or her particular requirements; and you
should only use any treatments described here with the full knowledge and
approval of your vet. No responsibility can be accepted.
If your cat
appears to be in pain or distress, do not waste time on the internet,
contact your vet immediately.
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