What is meant by the terms “Chronic Kidney Disease” and "Chronic Kidney Failure"?
The term
"chronic kidney failure" suggests that the kidneys have stopped
working and are, therefore, not making urine.
However, by definition, kidney disease is the inability of the kidneys
to remove waste products from the blood.
This definition can occasionally create confusion because some will
equate "kidney failure" with "failure to make urine". Kidney disease is NOT the inability to make urine. Ironically, most cats in kidney failure
are actually producing large quantities of urine, but the body’s wastes are
not being effectively eliminated. This is why many people avoid the term "kidney failure" and prefer "kidney disease". Because the kidneys are so efficient at their job and because cats are so adept at hiding their illnesses, it has been determined that a cat can lose up to 75% of normal kidney function before they begin to act sick. This is one reason that annual checkups with your veterinarian are so important!
There does come a point in CKD at which a cat's kidneys have been destroyed to the point where urine is no longer produced (anuria), but hopefully, the problem is recognized, discussed and treated before this is the case.
When is this likely to happen in my cat?
Commonly, chronic
kidney disease is considered to be the result of aging - a “wearing out”
process.
Most of the time, when chronic kidney disease is diagnosed, the cause is unknown. Biopsy of the chronic kidney usually results in a non-specific assessment called "chronic interstitial nephritis" - a hardening and inflammation of the filtration structures in the kidney.
There are some known contributing factors to kidney disease:
- Polycystic Kidney Disease: an inherited disease seen in certain purebreds where one or more fluid-filled cysts start to gradually replace normal kidney tissue
- Kidney tumors: lymphoma is a common type of cancer seen in cats, and it can affect many different organs, including the kidneys. White Blood Cells called lymphocytes become affected and interfere with normal kidney structure
- Infections: bacterial infection of the kidneys (known as 'pyelonephritis') may cause enough damage to the kidneys to cause CKD. Kidney infections are usually a complication of a long-standing, untreated urinary tract infection, but can occur more quickly in older cats with dilute urine, cats on immunosuppressive drugs, or cats with concurrent diseases such as diabetes or FIV.
- Toxins: certain toxins and drugs can damage the kidneys - for example, cats that eat plants from the lily family, drink antifreeze or ingest pills from the pain-reliever family like acetominophen or ibuprofen
- Glomerulonephritis: there are small filtration units in the kidneys called "glomeruli" that filter toxins from the bloodstream. These filters can become inflamed for
a variety of reasons and if the inflammation is prolonged, this can lead to CKD
For most cats, the early signs
occur at about 10-14 years of age. However, some cats may experience early onset kidney disease at 5-7 years or younger. About 20-50% of cats will be diagnosed with CKD at some time in their lives.
What changes are likely to occur in my cat?
The kidneys are the body's
filters, removing toxins from the blood and excreting them in the urine. When aging causes the
filtration process to become inefficient and ineffective, blood flow to the
kidneys is increased in an attempt to increase filtration.
This results in the production of more
urine.
To keep the cat from becoming
dehydrated, due to increased fluid loss in the urine, thirst is increased so
the cat drinks more water.
Other job functions of the kidneys:
- Maintaining hydration - the body's water balance
- Maintaining balance of salts and electrolytes
- Maintaining the acid balance of the body
- Maintaining normal blood pressure
- Producing hormones involved in calcium processing, red blood cell production, blood clotting and immune system health
Early signs of CKD:
- increased water consumption (polydipsia)
- increased urine production (polyuria) with or without litterbox avoidance
- mild or gradual weight loss
Signs of more advanced kidney disease include:
- loss of appetite/severe or rapid weight loss
- depression or lethargy
- vomiting
- diarrhea
- poor coat
- anemia
- very bad breath (uremia)
- occasionally, ulcers will be found in the mouth
Additionally, cats with kidney disease tend to have associated
high blood pressure.
How is chronic kidney disease diagnosed?
The diagnosis of kidney disease
is made by determining the level of two waste products in the blood:
blood urea nitrogen (BUN) and blood
creatinine.
A urinalysis is also
needed to complete the study of kidney function, with special attention paid to the "specific gravity" of the urine. Urine specific gravity is a measure of the "stuff" (such as proteins) in the urine that make it different than water. Since cats are descended from desert animals, they are very good at concentrating their urine - eliminating a lot of "stuff" and conserving a lot of water. Average specific gravity of cat urine is greater than 1.035, and may be as high as 1.060 if they eat a dry-food only diet. If the urine specific gravity drops below 1.035, it can be a red flag that indicates the cat is not concentrating urine well for some reason - for example: drinking more water than usual or losing kidney function. Comparing the BUN and creatinine levels in the blood to the urine specific gravity can be very informative to the veterinarian.
Although BUN and creatinine
levels reflect kidney failure, they do not predict it. A cat with marginal kidney function may have
normal blood tests. If that cat is
stressed with major illness or surgery, the kidneys may fail, sending the blood
test levels quickly into the abnormal range. Additionally, other factors can affect the body's BUN and creatinine levels, such as kidney infection, hyperthyroid disease, muscle loss, and anorexia (lack of food intake).
Since this is basically just a wearing out process, can it be treated
with anything other than a kidney transplant?
Yes, it can. We must recognize
that your cat’s kidneys have reached this point due to aging, so they will
never be normal again, but many cats still have enough functional kidney tissue
so treatment can be very rewarding.
Treatment generally has two phases. If your cat has reach a crisis, the first
phase is to “restart” the kidneys.
The cat is hospitalized and large quantities of intravenous fluids are given to “flush out” the
kidneys. This flushing process, called diuresis,
helps to stimulate the kidney cells to function again. If enough functional kidney cells remain,
they may be able to adequately meet the body’s needs for waste removal. Fluid therapy includes replacement of
various electrolytes, especially potassium.
Other important aspects of initial treatment include proper nutrition
and drugs to control vomiting and diarrhea.
There are some exciting new developments in diagnosis and treatment of feline chronic kidney disease that will hopefully be very beneficial when they become available outside of university research settings.
A
newly discovered biomarker of kidney disease may provide earlier detection and allow for closer monitoring and better, earlier treatments.
Stem cell therapy has been showing some promise in treating feline kidney disease, too. The stem cells for this therapy are cultivated from the fat of young, healthy cats; donor animals are not harmed.
What can I expect from this phase of treatment?
There are three possible outcomes
from the first phase of treatment:
1) The kidneys will resume functioning and
continue to function for a few weeks to a few years.
2) The kidneys will resume functioning during treatment but fail
again as soon as treatment stops.
3)
Kidney function will not return.
Unfortunately, there are no reliable tests that will predict the
outcome. The best your veterinarian can
do is assess the response of the cat's blood values and attitude while hospitalized and draw on their experience as to whether they recommend continued treatment, and if so, how aggressive that treatment needs to be to keep your cat healthy. A close relationship with your veterinarian will help them design a continuing treatment plan to keep your cat feeling healthy for as long as possible. That plan will need to be continually adjusted based on your cat's progress.
If the first phase of treatment
is successful, what happens next?
The second phase of treatment is
to keep the kidneys functioning as long as possible. This is accomplished with
one or more of the following, depending on the situation:
1. A high quality diet. This helps to keep the blood
tests as close to normal as possible, which usually makes your cat feel
better. We can recommend a commercially
prepared food that has the quantity and quality of protein needed by your
cat.
2. Potassium
supplementation. Potassium is lost in
the urine when urine production becomes excessive. A potassium supplement will replace that loss. Low potassium levels have been shown to
further reduce kidney function. This is
the second reason that a potassium supplement is recommended. Monitoring of your cat’s potassium will
guide our decision to supplement.
3. A phosphate binder. One of the secondary things that occurs in
kidney failure is an elevation of the blood’s level of phosphorus. This also contributes to lethargy and poor
appetite. Certain drugs will bind
excess phosphates in the intestinal tract so they are not absorbed, resulting
in lower blood levels of phosphorus.
Phosphate binders are helpful only when feeding a phosphate restricted
diet, as there is far too much phosphate in a
“normal diet” for these binders to be of benefit.
4. Fluids given at home. Once your cat is stabilized, fluids can be
given under the skin (subcutaneously). This serves to continually “restart” the
kidneys as their function begins to fail again. This is done once daily to once weekly, depending on the degree
of kidney disease. Although this might
not sound like something you can do, you will be surprised at how easily the
technique can be learned and how well most cats will tolerate it.
5. A drug to regulate the
parathyroid gland and calcium levels.
Calcium and phosphorus must remain at about a 2:1 ratio in the
blood. The increase in blood phosphorus
level, as mentioned above, stimulates the parathyroid gland to increase the
blood calcium level by removing it from bones.
This can be helpful for the sake of the normalizing calcium:phosphorus
ratio, but it can make the bones brittle and easily broken. Calcitriol can be used to reduce the function of the parathyroid gland and
to increase calcium absorption from the intestinal tract.
6. A drug to stimulate the bone
marrow to produce new red blood cells.
The kidneys produce erythropoietin, a hormone that stimulates the bone
marrow to make red blood cells.
Therefore, many cats in kidney failure have a low red blood cell count,
anemia. Epogen, a synthetic form of
erythropoietin, will correct the anemia in most cats. Unfortunately for some cats, the drug cannot be used long term
because the immune system recognizes the drug as "foreign" and will
make antibodies (immune proteins) against it.
How long can I expect my cat to live?
The prognosis is quite variable depending on response
to the initial stage of treatment and your ability to perform the follow-up
care. However, we encourage treatment
in most situations because many cats will respond and have good quality life
for up to 4 years.
