Kidney disease refers to the inability of the kidneys to work properly. Kidneys perform several key functions in the body, the most important of which is filtering waste products from the blood. Kidneys also maintain the balance of electrolyte levels in the body (such as sodium, potassium, and chloride), maintain blood pressure, and produce urine. Damage to the kidneys can result in the buildup of waste products to dangerous levels in the blood, also known as azotemia.
There are two main types of kidney disease – acute kidney injury (AKI) and chronic kidney disease (CKD). CKD develops slowly over time and can damage the kidneys to the point where they are unable to function properly. CKD was previously termed chronic renal failure (CRF). Unlike acute kidney injury, CKD does not disappear with treatment. CKD affects up to 10% of elderly dogs, while all cats are at risk of developing the disease. Unfortunately, it can take months or even years before a pet with CKD show signs of the disease. In addition, pets that have been diagnosed with AKI are at risk of developing permanent damage to their kidneys which can lead to CKD.
Chronic kidney disease can occur as a result of conditions that injure the kidneys. For example, kidney infections, urethral obstruction, and even tumors can result in the development of CKD. CKD can be congenital or present at birth. In many dogs and cats, the cause of CKD cannot be determined. Dogs and cats can develop CKD at any age, although it is more frequent in older populations. Cats over the age of 10 in particular are more at risk, with some statistics reporting a prevalence of 80% in geriatric cat populations.
Certain breeds are also thought to be more predisposed to CKD as well. These breeds for dogs include:
- Bull terrier
- Cavalier King Charles spaniel
- English Cocker spaniel
- Shar Pei
- West Highland white terrier
- Shih Tzu
Breeds more at risk for CKD in cats include:
- Maine Coon
- Russian Blue
CKD develops slowly and pets often do not show any clinical signs during early stages of the disease. Blood tests may identify CKD before clinical signs are obvious. The earliest signs of CKD include excessive thirst and increased urination. As the disease progresses, clinical signs include:
In order to diagnose kidney disease, your veterinarian will review your pet’s medical history, perform a physical examination, check the results of bloodwork and urine tests, and may even order an abdominal x-ray and ultrasound. A biopsy of the kidney maybe necessary to confirm the diagnosis in some pets. Not only do these tests allow your veterinarian to diagnose your pet with kidney disease, but they are also used to monitor the progression of CKD and any complications that may arise.
Medical history – your veterinarian will ask if there have been any changes in your pet’s behavior, such as their water intake, frequency of urination, and appetite. Physical changes, such as a change in body weight, will also be considered. Your veterinarian may also ask about your pet’s diet, current medications, and any previous illnesses or conditions.
Physical examination – your veterinarian will feel your pet’s kidneys. Your pet’s blood pressure will also be taken during the physical exam as 20% of dogs and cats with CKD have hypertension (high blood pressure), which can also further damage the kidneys.
Bloodwork – blood tests used to diagnosis kidney disease measure blood urea nitrogen (BUN) and creatinine values. Both BUN and creatinine are waste products which become concentrated in the blood as the kidneys lose the ability to filter them out properly. Elevated levels of BUN and creatinine may also indicate a kidney infection or dehydration rather than chronic kidney disease. Unfortunately, by the time BUN and creatinine are above normal levels, the kidneys have lost approximately 75% of their function. Along with BUN and creatinine, there is a newer blood test that is now being used which measures the value of symmetric dimethylarginine (SDMA) in the blood serum. An increase in SDMA concentration can indicate the presence of kidney disease much earlier than traditional tests when the kidneys have only lost about 40% of their function rather than 75%. Anemia is a common comorbidity in kidney disease and a complete blood count will help to monitor for anemia.
Urine testing – a urinalysis is able to measure the appearance, pH, concentration, and levels of different substances in the urine. A urine specific gravity (USG) measurement assesses how concentrated the urine is. For cats diagnosed with chronic kidney disease, USG is neither dilute nor heavily concentrated – instead, it will fall in the middle range known as isothenuric as the kidneys are no longer able to properly dilute or concentrate the urine as needed. As a lower USG measurement is not uncommon in healthy dogs, it is a less reliable indicator of kidney disease.
Diagnostic imaging – in pets with chronic kidney disease, the kidneys may shrink in size and firm up from scarring. An abdominal x-ray will allow the veterinarian to determine the size of the kidneys, while an ultrasound can provide additional insight into the kidneys’ inner structure. Abdominal ultrasound is the typical diagnostic test for kidney tumors.
Veterinarians use a standardized grading scale to classify the severity of CKD and streamline treatment protocols. The following grading scale is broken into four stages to address pets with CKD:
- Stage I – no signs of azotemia (buildup of toxins in the blood); normal level of creatinine in the blood and a normal or mild increase in the level of SDMA; other abnormalities of the kidneys may be present.
- Stage II – mild azotemia is present; normal or mild increase in level of creatinine; mild increase in the level of SDMA; there may be increased water in the urine and an increase in the volume of urine.
- Stage III – moderate azotemia is present; increased levels of creatinine and SDMA; pet begins to develop signs of disease.
- Stage IV – severe azotemia is present; high levels of creatinine and SDMA; pet shows signs of being extremely sick.
For more information on how CKD is staged in pets, visit the International Renal Interest Society (IRIS) website.
In order to determine proper treatment, your veterinarian will need to establish whether the kidney disease is acute or chronic, as well as the underlying cause if one can be found. Unfortunately for pets with chronic kidney disease, there is no cure. Treatment for CKD is focused on managing the clinical signs and maintaining a good quality of life at each stage of the disease. Any underlying causes or additional complications, such as high blood pressure or infections, will be treated as well.
Fluids – as kidneys are responsible for regulating the balance of water in the body, damaged kidneys may become unable to excrete excess body fluids leading to overhydration, or instead, the kidneys may produce too large quantities of urine leading to dehydration. For pets with CKD at risk for dehydration, your veterinarian will recommend increasing the amount of fluid your pet takes in at home. Switching from dry food to canned or adding water or chicken broth to your pet’s meals will boost fluid intake. Your veterinarian may even prescribe subcutaneous (SQ) fluid administration, in which fluids are injected directly under your pet’s skin. For information on how to administer SQ fluids in cats, check out the video with step-by-step instructions from atdove.org.
Diet – your veterinarian will prescribe kidney-friendly food which contains less protein than regular pet foods. That way, the kidneys will not have to work as hard filtering out the waste products in the blood from protein metabolism. These specialized diets are also often supplemented with B vitamins, potassium, omega-3 fatty acids, and antioxidants. As elevated blood phosphorus levels have been associated with shorter survival in pets with CKD, these diets also tend to be low in phosphorus in order to restrict intake.
Medications – your veterinarian may prescribe medication in order to treat other complicating factors related to your pet’s CKD. These may include phosphate binders (which prevent phosphorus from being absorbed from your pet’s food), high blood pressure medication, medications to stimulate bone marrow production of red blood cells, appetite stimulants, and anti-nausea medication.
Monitoring – your veterinarian will want to schedule follow-ups frequently depending on the severity of your pet’s CKD. Your pet will go through a physical examination, have bloodwork and urine testing done, and have their treatment plan reevaluated. Appointments may be made every 3 to 6 months for pets in Stages II or III and may be made every 1 to 3 months at Stages III and IV.
Dialysis – hemodialysis purifies the blood of any waste products normally filtered out by the kidneys. Dialysis is used to stabilize severely sick patients while the kidneys recover and is usually only used if there are extremely high levels of toxins in the blood, a severe imbalance of electrolytes, and if the patient is overhydrated and unable to produce urine. Dialysis can prolong life and will require a discussion with your veterinarian if it is a feasible treatment option for your pet.
The best method of prevention is early detection. Unfortunately, CKD has no cure, but pets diagnosed with this disease can have a good and prolonged quality of life if caught early and managed correctly.