Chronic Kidney Disease and Failure (CKD, CRF, CRD)
Chronic kidney disease is defined as kidney disease that has been present for
months to years. Chronic renal disease (CRD), chronic renal failure (CRF), and
chronic renal insufficiency refer to the same condition.
CKD is not a single disease. There are many different causes of CKD but by the
time the animal shows signs of kidney disease the cause may no longer be
apparent. Some potential causes of CRF include:
- congenital malformation of the kidneys (birth defects)
- chronic bacterial infection of the kidneys with or without kidney stones
- high blood pressure (hypertension)
- diseases associated with the immune system (e.g. glomerulonephritis,
- acute kidney disease, for example poisoning with antifreeze, that damages
the kidneys can lead to CKD
Often the cause of CKD is unknown.
Structure of the kidneys
The microscopic unit of the kidney is called the nephron. Each kidney
contains thousands of nephrons. When the pet is young and healthy not all
nephrons are working all of the time; some nephrons are held in reserve. As the
animal ages or if the kidneys are damaged, some nephrons die and other resting
nephrons take over the work of those that die. Eventually all the remaining
nephrons are working. When there are no extra nephrons remaining and kidney
damage continues the pet will start showing signs of CKD. Because of this
stepwise loss of nephrons the kidneys are able to "hide" the fact that they are
damaged until the damage is severe. When 2/3 of the nephrons have been lost the
pet is no longer able to conserve water and the pet passes larger amounts of
dilute urine. By the time a pet has an elevation in the waste product creatinine
in its blood, 75% of the nephrons in both kidneys have been lost.
What do the kidneys do?
When blood flows through the kidneys, the kidneys act as a complex filter
that removes from blood wastes that are generated from break down of food, old
cells, toxins or poisons and many drugs that are given for treatment of other
diseases. The wastes are removed with water as urine. Waste products than can be
measured in the blood include creatinine and urea nitrogen but there are many
other waste products that are not measured by blood tests. The kidneys also acts
as a filter to keep "good" substances in the blood. The kidneys regulate the
amount of water in the blood by excreting extra water and retaining water to
prevent dehydration by varying the amount of urine that is produced. The kidneys
help regulate blood pressure by saving or eliminating sodium based on how much
sodium the pet is eating. The kidneys help regulate calcium and vitamin D which
keep bones strong. The kidneys produce a substance that helps with the creation
of new red blood cells. Because the kidneys have so many functions, when the
kidneys are not working normally, there are many signs that the pet may show.
CKD is progressive
By the time the pet shows signs of CKD, the damage is severe. There is no
cure for CKD. The remaining nephrons are working so hard that with time they
will fail as well. CKD is usually fatal in months to years but various
treatments can keep the pet comfortable and with a good quality of life for
months to years.
Signs of CKD
Because the kidneys perform so many functions, the signs pets with CKD show can
vary quite a bit. The signs may be severe or may be subtle and slowly
progressive. Despite the chronic nature of the disease, sometimes signs appear
suddenly. Some of the more common signs of CKD include:
- drinking too much (polydipsia) and urinating large volumes of urine
- the increased volume of urine in the bladder may lead to, or worsen
incontinence (leaking urine), especially at night
- vomiting and/or diarrhea
- lack of appetite and weight loss
- general depression related to the elevation of waste products in the blood
- anemia resulting in pale gums and weakness due to a low blood count
- overall weakness from low blood potassium
Less common signs include
- weakened bones can result in bone fractures
- high blood pressure can lead to sudden blindness
- itchy skin from calcium and phosphorous depositing in the skin
- bleeding into the stomach or gut or bruising of skin
Signs you may
see if you examine your pet include: dehydration, weight loss, pale gums and
ulcers in the mouth.
The signs seen in pets with CKD and the findings on examination are not
specific for CKD and may be seen with many other diseases so blood and urine
tests are needed to make a diagnosis of CKD.
Abnormalities that are often seen on diagnostic blood and urine tests
- anemia without signs of a response by the body to the low blood count (non
- increased wastes that are normally removed by the kidneys (blood urea
nitrogen [BUN] and creatinine)
- increased phosphorus
- calcium is often normal but can be elevated in some pets with CKD and rarely
- dilute urine
- +/- protein or bacteria in the urine
Sometimes bruising occurs where the blood sample was drawn as pets with CKD
may have platelets that are less sticky than normal (normal platelets prevent
A diagnosis of CKD can usually be made based on the signs, physical
examination and blood and urine tests but other tests may be performed to look
for an underlying cause for the CKD and/or to "stage" the CKD.
The severity of chronic kidney disease (CKD) can be estimated based on blood
waste product elevation and abnormalities in the urine such as the presence of
protein. The International Renal Interest Society (IRIS) has developed a method
to estimate the stages of CKD. Stages are numbered 1 through 4 where one is the
least severe and four is the most severe. The higher the stage number also
generally corresponds to the greater number of symptoms seen in the pet.
Some treatments are recommended to be started when the pet has a certain stage
IRIS site for full details on staging
Other tests that may be performed include
- Determination of kidney size using abdominal radiographs (x-rays) or
What might this test show?
The kidneys in pets with CRD are usually small reflecting the death of
a large number of nephrons. If the kidneys are large then certain causes for the
CKD should be considered such as lymphoma (cancer) of the kidneys, or an
uncommon disease called amyloidosis. Some pets with signs of kidney disease who
have large or normal sized kidneys may have acute kidney failure rather than
CKD. The treatment and prognosis for pets with acute kidney disease differs from
the treatment and prognosis of pets with CKD.
- Kidney biopsy
What might this test show? A biopsy is not
required to make a diagnosis of CKD but the results of a biopsy may show a cause
for the CKD. A biopsy is more likely to show specific information when the
kidneys are big rather than small. A biopsy can be valuable in pets who develop
CKD at a young age or who are of a breed known to develop congenital kidney
disease. There may be specific microscopic changes in a kidney biopsy from an
animal with congenital kidney disease that may suggest that related animals are
also at risk for developing CKD. Knowledge that the cause of CKD is caused by
congenital kidney disease does not change the treatment of the affected animal
but does provide information for related animals, for example if you should
remove them from a breeding program. When a biopsy is planned, usually the
biopsy is collected using ultrasound or laparoscopy to see the kidney during the
biopsy so that no other organs are damaged during the biopsy.
- Bacterial culture
What might this test show?
Bacterial infection is not a common cause of CRD but pets with CKD may
develop a bacterial infection as several aspects of the pet's immune system may
be less functional when the kidneys are failing. If white blood cells are
observed on microscopic examination of the pet's urine, a bacterial culture of
the urine should be obtained.
- Tests of clotting ability
What might this test show? If a pet is going
to under go kidney biopsy, tests may be performed in advance to evaluate the
ability to stop the bleeding from the biopsy site.
Treatment of CRF
The severity of the pet's signs will determine what treatments are needed.
Not all treatments presented below may be needed or appropriate for each pet
with a diagnosis of CKD. Treatments may also be started incrementally (a few
treatments are started and then based on patient response, additional treatments
may be added later). The information below is not
meant to be a substitute for veterinary care.
Pets with severe signs may be hospitalized for fluid and intravenous drug
treatment to reduce the amount of waste products in their body. Many pets with
CKD will feel better in response to treatment with IV fluids but if the kidney
disease is extremely severe the pet may not respond to treatment.
Those pets who are still eating and not showing severe signs are treated with
a variety of treatments, often introducing treatments incrementally as new signs
develop. The treatment approach is often called "conservative" compared to more
aggressive treatments such as hospitalization for fluid therapy, dialysis or
kidney transplantation. Remember that CKD is not a disease that can be
Treatments are designed to reduce the work the kidneys need to perform,
to replace substances that may be too low (such as potassium) and to reduce
wastes that accumulate such as urea (generated by the body from proteins) and
phosphorus. The initial response to conservative therapy may be relatively slow,
taking weeks to months to see a response.
Feeding of a kidney diet is usually recommended. Kidney diets contain
less protein compared to other diets and the protein is high in quality. It is
protein in the diet that is converted to waste products that the kidneys must
remove in the urine. The higher the quality of the protein in the diet, the less
wastes created for the kidneys to eliminate. Low quality protein requires the
kidneys remove more wastes. which makes them work harder. Egg and meat contain
higher quality protein; cereal grain protein is of lower quality which leads to
more wastes for the kidneys to eliminate. Protein is used by the body to repair
cells and tissues that are continually regenerating, so a pet needs some protein
in their diet. By feeding a low quantity, but high quality protein diet that
contains an appropriate amount of fats and carbohydrates, the pet's body can use
the protein for replacing the cells and tissues and use the fat and
carbohydrates for energy. Kidney diets also contain a lower amount of
phosphorus. Phosphorus accumulates in the blood when the kidneys are diseased.
Kidney diets control the amount of other substances that may be too high or too
low in patients with CKD such as salt, potassium, magnesium and B vitamins.
There are differences in the kidney diets for dogs and cats. When making diet
changes it is often beneficial to gradually introduce the new diet by adding
increasing amounts of the new diet while reducing the amount of the current diet
over 1 to 2 weeks. The pet is more likely to accept a new diet when it is
introduced gradually and it is less stressful to the kidneys to gradually adapt
to changes in the diet.
Protein restricted diets are less palatable than higher protein diets. Pets
with CKD that are still eating are more likely to accept a change in diet to a
protein restricted diet than are pets who are very ill and refusing most foods.
Protein restricted diets are more expensive than higher protein diets.
There are many pet food companies that sell kidney diets. Dr. Tony
Buffington at the Ohio State University is a good source of information on
http://vet.osu.edu/1442.htm select a species, a diet form and select
Reduced Phosphorous/Protein for a list of diets for pets with kidney
disease. Homemade diets can be fed but it is best to work with your veterinarian
to formulate a diet that is balanced.
(click to expand for published information about diet
in pets with CKD)
It is generally agreed that feeding renal failure diets to dogs and cats with
kidney disease improves their quality of live and may
minimize the progression of the
disease resulting in a longer life span. Studies that evaluate the effect of
dietary changes on quality and quantity of life typically use commercial diets
that differ in their composition of protein, phosphorus, sodium and lipids
compared to maintenance diets so that positive effects are not attributable to a
single component of the diet but rather to a "diet effect
A randomized, double masked, clinical study in 38 dogs with spontaneous stage
3 or 4 kidney disease, half of which were fed a kidney failure diet and the
other half a maintenance diet, published in
JAVMA in 2002, demonstrated improved quality and increased quantity of life
in the group fed the renal failure diet.
- The median interval before development of a uremic crisis was twice as long
in the group fed the renal diet
- Dogs fed the renal diet survived at least 13 months longer (average 593 vs
- Owners of dogs fed the renal diet reported significantly higher quality of
life scores for their dogs
The results of a
study of cats with naturally occurring stable chronic renal failure fed a
diet restricted in phosphorus and protein compared to cats with CKD fed a
maintenance diet reported a median survival of 633 days for 29 cats fed the
renal diet compared to 264 days for 21 cats fed a regular diet. The groups were
not randomly determined but based on cat & owners willingness to change to the
In a study published in
JAVMA in 2006, 45 client-owned cats with spontaneous stage 2 or 3 CKD were
randomly assigned to an adult maintenance diet (23 cats) or a renal diet (22
cats) and evaluated for up to 24 months. Findings included:
- Significant differences: BUN lower and blood bicarbonate higher in the renal
- No Significant differences
urine protein-to-creatinine ratio
parathyroid hormone concentrations.
- 26% of cats fed the maintenance diet had uremic episodes (26%), compared
with 0% cats fed the renal diet
- At the conclusion of the study, 5 (21.7%) cats in the maintenance diet group
had died from renal causes and there were no renal-related deaths in the renal
- There were no significant differences in quality of life as perceived by
owners responding to a questionnaire.
- Owners impressions of cats willingness to consume the diets did not differ
Because pets with kidney disease cannot conserve water by making
concentrated urine, their water intake is very important to prevent dehydration.
Make sure they always have plenty of fresh water available. If the pet is not
eating well, or is vomiting, then s(he) may not be drinking enough and may get
dehydrated. Pets can be encouraged to drink by giving them flavored broths in
addition to plain water. The broth should be low in sodium and its best to
discuss with your veterinarian other ingredients in the broth to make sure it
doesn't contain substances that will make the kidneys work harder.
Water soluble vitamins
like B and C are lost in greater amounts when the pet is urinating greater
amounts. Kidney diets contain increased amounts of water soluble vitamins so
additional vitamins do not need to be given unless a homemade diet is being fed.
Lack of appetite and increased loss of potassium in urine may result in
low body potassium (hypokalemia). Cats with CKD are more likely to have low
body potassium than are dogs. Cats with low potassium may develop painful
muscles. Both cats and dogs may be weak when potassium is low. Cat kidney diets
contain higher levels of potassium so additional supplementation is probably not
needed unless the cat shows signs of muscle pain. Potassium gluconate or
citrate can be given by mouth if potassium supplementation is needed. Potassium
chloride is acidifying and is not recommended.
Phosphorus, calcium and PTH
Pets with CKD usually have increased blood phosphorus. In health,
phosphorus and calcium are controlled by a hormone called parathyroid hormone
(PTH). PTH works with vitamin D on the intestine, kidney and bone to keep
calcium and phosphorus normal. As the kidneys fail the amount of PTH in the
body is elevated and the amount of vitamin D is reduced. Elevated PTH itself may
be responsible for some of the signs shown by pets with CKD. PTH draws calcium
and phosphorus from the bones which can weaken bones which can lead to bone
Kidney diets typically contain reduced phosphorus and an appropriate amount of
calcium but if phosphorus remains elevated when the pet is eating a kidney diet
then phosphorus can be tied up in the intestinal tract so it can be eliminated
in the stool. Intestinal phosphate binding agents include aluminum carbonate,
aluminum hydroxide, aluminum oxide, calcium citrate, calcium acetate and calcium
carbonate and sevelamer hydrochloride. Phosphate binding agents which contain
calcium should not be used until blood phosphorus is normal to prevent calcium
and phosphorus from combining and precipitating in tissues including the
kidneys. It is not usually necessary to give additional calcium but if a pet has
low blood calcium, the phosphorus should be normalized before giving calcium.
Even when blood phosphorus is normalized, PTH levels are still higher than
The administration of low doses of vitamin D (1, 25
dihydroxycholecalciferol [calcitriol]) will suppress PTH and possibly slow the
rate of progression of kidney deterioration.
It is not 100% agreed that giving your
pet calcitriol will slow the deterioration of the kidneys.
Here are some web sites on using
Some pets with CKD will have an acid blood pH. Kidney diets are
designed to counteract the acidosis but very sick animals that are hospitalized
may need addition treatment to correct the acidosis.
Diseased kidneys are less efficient at regulating sodium and sodium in
turn helps control blood volume and pressure. Excess sodium can lead to water
retention and not enough sodium can lead to dehydration. When changing diets
that contain different amounts of sodium (kidney diets usually have less sodium
than regular diets) make the change gradually over several weeks. Use caution
when giving your pet table scraps or treats that may be high in sodium.
High blood pressure (hypertension)
Many pets with CKD have high blood pressure. High blood pressure can contribute
to further decline of kidney function and can occasionally lead to sudden
blindness from retinal detachment. Ideally blood pressure should be measured by
your veterinarian and hypertension confirmed before giving drugs to treat high
blood pressure but measuring true blood pressure in dogs and cats can be
difficult. If the pet has an elevation in blood pressure it may be due to the
excitement of being examined or due to CKD. The calmer you are able to keep your
pet during examination, the more reliable the readings for blood pressure. There
are several drugs that may be used to manage high blood pressure including
enalapril, benazepril, or amlodipine (and others). Enalapril and benazepril are
in a class of drugs called
ACE inhibitors and are sometimes used in pets with CKD that have abnormal
amounts of protein in their urine even when blood pressure is normal.
The kidneys play a role in producing a hormone called erythropoietin
which stimulates the production of new red blood cells. Red blood cells live
about a hundred days so new cells are continually being made. Less
erythropoietin is made in pets with CKD leading to anemia. The packed cell
volume (PVC) (also called hematocrit) is the percentage of blood cells compared
to fluid in whole blood. When the PCV is ~20 in cats and ~ 25% in dogs, anemia
may contribute to lack of activity and weakness.
Anemia can be treated by blood transfusion or by the administration of human
erythropoietin. Erythropoietin is very effective in increasing PCV but because
human erythropoietin is not exactly the same as dog and cat erythropoietin, over
time, the pet may form antibodies that cause the medication to become
ineffective. Canine and feline erythropoietin are currently being studied.
Certain types of fats (polyunsaturated omega 6 fatty acids) may slow
the decline in kidney function are are often present in kidney diets.
Some cats and dogs with kidney disease may not drink enough to prevent
becoming dehydrated and may benefit from the administration of intermittent SC
fluids. If your veterinarian feels your pet may benefit from giving subcutaneous
fluids, we provide some instructions on how to give SC fluids. See
Lack of Appetite
The accumulation of wastes in the body often decreases appetite. A goal
of several of the above treatments is to reduce the amount of wastes in the
blood. If the pet remains off food despite above treatments you might try
different brands of renal failure diets, warming the food or adding odiferous
toppings to entice the pet to eat.
Increased levels of waste products cause
the pet to vomit. Your veterinarian may recommend
medications that reduce nausea or act directly on
brain centers to reduce the urge to vomit.
Drugs used to treat other diseases
Because the kidneys are responsible for elimination of many drugs, make sure
that your veterinarian is aware of any other medications you are giving your pet
as these may accumulate in the body to toxic levels if the kidneys cannot
If the urine shows signs of infection or if a urine
culture grows bacteria then antibiotics may be administered. If a urinary tract
infection is involving the kidneys, the period of treatment is much longer than
a infection of the bladder.
You are in the best position to judge what is stressful to your pet. When a
pet is stressed they may drink and eat less than normal. Reduced water intake is
detrimental to diseased kidneys. When possible, keep your pet calm. That might
mean for example: having an in-home pet sitter if your pet is stressed by
boarding, removing the pet from the household during a party or limiting contact
with other animals if these situations appear to be a source of stress for your
pet. Extremes in heat or cold are stresses. Certain drugs such as
prednisone/cortisone make the kidneys work harder.
There has been progress made in transplantation of kidneys, more for cats
than for dogs.
http://www.felinecrf.com/transb.htm for a list of facilities that currently
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