Chronic kidney disease, or CKD, is one of the most prevalent diseases in older pets, affecting up to 40% of cats over the age of 10 and up to 10% of geriatric dogs. Healthy kidneys perform many essential functions for our pets, including filtering the blood, making urine, and helping to regulate blood pressure. CKD refers to the persistent loss of kidney function over time and can have many health consequences. The only known risk factor for the development of CKD in cats and dogs is age, so it is very important for all senior pets especially cats to be regularly monitored for this disease.
Clinical Signs
In the early stages of CKD, it is very common for cats and dogs to show no obvious clinical signs, as their bodies are able to compensate for the gradual decrease in kidney function. But as the disease progresses clinical signs will emerge: as the kidneys lose their ability to concentrate urine effectively, pets may begin to urinate greater volumes and more often and drink more water to compensate. The loss of important proteins and vitamins in their urine may contribute to abnormal metabolism and loss of appetite. Eventually, pets with CKD may experience a build up of the waste products and other compounds in the bloodstream that are normally removed or regulated by the kidneys. This accumulation may make them feel nauseas and appear lethargic, unkempt and lose weight.
Cats and dogs with CKD are also at risk for hypertension (high blood pressure) and anaemia (low red blood cell count). The kidneys play an important role in maintaining appropriate blood pressure, and this can be disrupted in patients with CKD. High blood pressure can lead to sudden changes in vision, neurologic abnormalities such as disorientation and weakness, or heart issues. The kidneys also normally produce a hormone known as erythropoietin, which is vital in the production of new red blood cells. Cats and dogs with CKD produce less of this hormone, leading to anaemia. Lack of red blood cells will cause pets to feel very lethargic, have a poor appetite, and have pale or white gums.
Diagnosis
To evaluate kidney function, veterinarians will most often turn to blood tests and urine analysis (urinalysis) to evaluate the concentrations of waste products and other components that healthy kidneys normally filter or regulate. It is important to note, however, that there is no single test that can give a veterinarian a complete picture of kidney function and prognosis. Which is why a combination of tests is often recommended.
Blood tests can determine the concentration of three important waste products normally filtered by the kidneys: blood urea nitrogen (BUN), creatinine, and symmetric dimethyl arginine (SDMA). An increase in the concentration of these compounds in your pets blood, also known as azotaemia, may suggest that their kidneys are not functioning properly, but these values must be interpreted in light of a number of factors. Creatinine has historically been recognized as the most specific indicator of kidney function, but this test has some limitations. Dehydration, for example, can cause BUN and creatinine concentrations to increase in spite of the fact that kidney function is normal. Muscle mass also affects creatinine concentrations, so a very thin cat may have normal blood creatinine levels despite decreased kidney function. SDMA concentrations are less affected by dehydration and muscle mass and also
rise earlier in the progression of CKD. Creatinine concentrations in the blood do not generally rise until a pet has lost almost 75% of their renal function, while SDMA elevations are detectable when about 40% of kidney function is lost, potentially allowing CKD to be diagnosed sooner.
In a urinalysis, your veterinarian will consider the concentration of the urine (urine specific gravity, or USG), its pH, and the presence of blood cells, bacteria, and other cells that generally should not be found in your pet’s urine, all of which provide important information regarding the health of their kidneys. A low urine specific gravity, indicating poorly concentrated urine, can be one of the earliest indicators of CKD. Urine protein/creatinine ratio, or UPC ratio, tests for protein loss through the kidneys and can be very important in determining the severity of disease. It is sometimes also important to culture a urine sample to rule out the possibility of bacterial infection of the urinary tract in suspected cases of CKD. Urine samples may be obtained either by free-flow collection, catheterization, or by cystocentesis (a technique that extracts a urine sample by passing a very fine needle through the abdominal
wall into the bladder). Cystocentesis is generally considered a safe procedure, and in most cases will provide the most diagnostically useful sample for analysis.
Ideally, a veterinarian will base their interpretation of kidney function on blood and urine samples, from a stable, well-hydrated animal. The concentrations of other blood components, including various electrolytes (like sodium and potassium), phosphorus, red blood cells, and proteins are also important to evaluate in a pet being examined for CKD. Other studies that can be useful in evaluating a pet with suspected CKD include imaging studies such as abdominal ultrasound, radiographs (X-rays), and, in some cases, microscopic evaluation of biopsy samples. Approximately 60% of pets with CKD will also develop hypertension, so measurement of blood pressure is an important part of the medical evaluation for this disease.
The International Renal Interest Society, or IRIS, has developed a staging system to categorize cats and dogs with CKD based on these testing parameters. It is important that the staging occurs when the patient is well hydrated and stable, as elevated values in a dehydrated or sick pet could make it appear that they are in a higher stage of disease than they truly are. With this in mind, appropriate staging can provide useful treatment and management guideline for owners and veterinarians, as well as prognostic information based on the severity of disease. Additional substage categories are considered as well, based on the presence or absence of protein in the urine and high blood pressure.
Treatment and Management
Unfortunately, CKD is a progressive disease with no definitive cure, so the goal of treatment is to slow its progression and maintain a good quality of life for the pet. Therapy is geared toward minimizing the build up of toxic waste products in the bloodstream, maintaining adequate hydration, addressing disturbances in electrolyte concentrations, supporting appropriate nutrition, controlling blood pressure, and slowing the progression of kidney disease.
Dietary modification is an important and proven aspect of CKD treatment, and generally the first change recommended early in the course of disease. Studies suggest that therapeutic diets that are restricted in protein, phosphorus and sodium content and high in water-soluble vitamins, fibre, and antioxidant concentrations may prolong life and improve quality of life in pets with CKD. Some studies show that cats with CKD eating a prescription kidney diet live 2-3 times longer than those eating a standard commercial cat food. However, many cats and some dogs have difficulty accepting therapeutic diets, so owners must be patient and dedicated to sticking to the plan. It is important to make a gradual transition to a therapeutic diet and to consider food temperature, texture, and flavour. Prescription diets for kidney disease come in a variety of flavours and textures and are available in both wet and dry formulations, so it is important to work closely with your veterinarian to find the best option for your cat or dog. Pets and especially cats with CKD that go without food for relatively short periods of time may develop significant health problems, so it is crucial to make sure that your pet is eating during a transition to a therapeutic diet.
Maintaining good hydration is essential for pets with CKD, as dehydration can speed up damage to the kidneys and cause clinical signs to worsen. At home, this can be encouraged by feeding wet forms of the therapeutic diet and ensuring access to multiple clean water sources. Some cats may even prefer to drink from a pet water fountain. Sometimes, administering fluids under the skin may be necessary to adequately hydrate cats and smaller dogs with CKD, especially those with advanced stages of disease. Many owners can learn to perform this at home every 1-3 days with guidance from their veterinarian. During times of illness, intravenous fluids administered in a veterinary clinic may be necessary to maintain hydration until a pet can be stabilized.
Managing related complications, such as hypertension, anaemia and urinary protein loss, are vital in slowing progression of CKD and improving quality of life. High blood pressure and urinary protein loss are generally treated with oral medications, such as angiotensin II receptor blockers known as telmisartan or benazepril. Anaemia in cats with CKD can be treated by hormone replacement therapy with erythropoietin injections which stimulates red blood cell production. A number of other therapies, including phosphate binders, potassium supplementation, antioxidant supplementation, appetite stimulants, and anti-nausea medications, have the potential to improve quality of life for pets living with this disease.
Prognosis
Prognosis for patients with CKD is quite variable and can depend significantly on their response to treatment and the stage of disease at the time of diagnosis. There is evidence suggesting that the earlier CKD is diagnosed and treatment initiated, the better the outcome with respect to quality of life and survival. For example cats who are diagnosed with IRIS Stage 2 CKD have a mean survival time of two to three years in many studies, while those who are diagnosed at IRIS Stage 4 on average survive less than 6 months even with aggressive treatment. These are, of course, averages, and regular monitoring is important to determine how quickly an individual’s disease is progressing. Chronic kidney disease is, unfortunately, a common problem in older cats. And cats are stoic creatures when it comes to showing signs of illness, they will often show no obvious clinical signs in the early stages of CKD, but early diagnosis remains the best chance for a longer and healthier life. This underscores the importance of regular veterinary exams and monitoring bloodwork for all senior pets.
