What do kidneys do?
The kidneys’ main functions are to remove waste from the bloodstream, conserve water, produce urine, and regulate the levels of certain essential minerals such as potassium and sodium.
What is chronic kidney disease?
Chronic kidney disease (CKD) is the inability of the kidneys to efficiently filter the blood of waste products. The kidneys have a large amount of spare capacity to perform their various functions, so at least two-thirds (67% to 70%) of the kidneys must be dysfunctional before any clinical signs are seen. In many cases, kidney damage has occurred over several months or years (chronic) before the disease is evident.
It is mainly a problem in mature and senior cats (seven years and older), affecting 30% to 40% of cats over 10 years of age and 81% of cats over 15 years. Only about 10% of cases occur in cats less than three years old.
What are the clinical signs of CKD?
Early signs of disease in cats are often dismissed as normal aging changes, and include:
- Weight loss
- Poor coat quality
- Variable appetite
- Increased water consumption and urination
In the initial stages of kidney failure, the kidneys produce a larger amount of more diluted urine to cope with their inability to efficiently remove waste products. Cats often drink more to compensate for the increased water loss. This stage is known as compensated kidney disease.
After approximately two-thirds of the kidney tissues fail, the amount of waste in the bloodstream increases quickly and severe disease seems to begin suddenly. In more advanced stages of CKD, signs include:
- Poor appetite
- Lethargy
- Depression
- Vomiting
- Diarrhea
- Anemia
- Bad breath that may be associated with mouth ulcers
What causes chronic kidney disease?
CKD is the end stage of various disease processes. It is most often associated with aging, and can be seen as the kidneys simply “wearing out.” Diseases and conditions that can eventually lead to CKD include:
- Congenital malformations of the kidneys (problems that the cat is born with), such as polycystic kidney disease in longhaired cats
- Pyelonephritis (bacterial kidney infections
- Glomerulonephritis (inflammation and damage to the kidney's filtration membrane)
- Neoplasia (tumors of the kidney), most commonly lymphosarcoma
- Amyloidosis (build-up of an unusual protein in the kidney that prevents it from functioning normally)
- Viral infections, such as feline leukemia virus (FeLV) and feline infectious peritonitis virus (FIP)
- Kidney stones or ureteral stones
How is CKD diagnosed?
Several blood and urine tests are needed to diagnose kidney disease:
- A urinalysis is required to evaluate kidney function.
- Urine specific gravity (USpG) is a test of urine concentration. A low USpG means the urine is diluted (watery), which is the earliest sign of kidney disease.
- Increased protein in the urine (proteinuria) indicates decreased kidney function.
- Cystatin B is a new test done on urine that may detect kidney damage before other tests. It may be useful in cases of suspected early or acute kidney injury.
- A blood biochemistry analysis assesses the function of various internal organs. Increased amounts of waste products in the blood indicate decreased kidney function. Products measured include:
- Blood urea nitrogen (BUN)
- Blood creatinine (CREAT)
- Symmetric dimethylarginine (SDMA)
- Red and white blood cell counts help determine the extent of kidney failure and the best course of treatment.
- Other tests measure blood levels of substances such as albumin, globulin, potassium, sodium, phosphorus, and calcium.
A cat with compensated chronic kidney failure with marginal kidney function may have normal levels of BUN and creatinine, with high normal to slightly elevated SDMA, and a low urine-specific gravity. If a major stress occurs, such as illness or surgery, the kidneys may fail quickly, increasing the blood test values. A cat diagnosed with low urine-specific gravity as well as elevated SDMA, BUN and CREAT is said to be azotemic.
How will my veterinarian determine the degree of kidney disease in my cat?
Your veterinarian will use the International Renal Interest Society (IRIS) staging system to assess your cat’s kidney disease. This system is based on blood creatinine levels, urine protein levels (measured with a urine protein: creatinine ratio, or UPC), and blood pressure. Staging helps your veterinarian choose the best treatment plan, monitor your cat’s condition, and estimate prognosis.
How is CKD treated?
CKD treatment depends on blood test results. Treatments aim to resolve specific abnormalities and slow disease progression. Most cats are effectively managed with diet change, including supplementation, and one or two other treatments. Your veterinarian will work with you to determine the best treatment for your cat.
- Therapeutic diets. Restricted protein and low phosphorus diets help reduce waste products in the bloodstream and decrease the workload on the kidneys. Prescription diets are available from your veterinary practice, including Hills k/d, Royal Canin Renal Support, and Purina NF. Your veterinarian will recommend the most appropriate diet for your cat.
- Phosphate binders. Cats with kidney disease may develop elevated blood phosphorus levels despite having low phosphate in the diet. Oral phosphate binders, such as aluminum hydroxide, help reduce phosphorus absorption through the gut wall, improving your cat's well-being and slowing disease progression.
- Antibiotics. Cats with CKD develop bladder infections more frequently, increasing the risk of kidney infections, so antibiotics are prescribed for these infections. Routine urine cultures are recommended for many patients.
- Potassium supplementation. Cats with kidney disease often lose too much potassium in the urine, leading to muscle weakness, stiffness, and poor hair quality. Low potassium levels may also contribute to the worsening of kidney failure. Potassium supplementation can offset these losses.
- B-vitamins. Failing kidneys cannot keep the urine concentrated, so water-soluble vitamins like B12 become depleted. Affected cats can benefit from vitamin supplements.
- Anti-nauseant medications, antacids, and appetite stimulants. These medications may help cats experiencing vomiting and reduced appetite. Anti-nauseants include maropitant (Cerenia®), antacids include omeprazole, appetite stimulants include capromorelin (Mirataz®).
- Blood-pressure lowering drugs. Many cats with kidney failure have high blood pressure, which can further damage the kidneys. Blood pressure medications may be prescribed as part of treatment.
- Medication to reduce proteinuria. Cats with protein in the urine (proteinuria) are at increased risk of CKD progression, so medication to treat this issue can slow progression.
- Hormone replacement for anemia. The kidneys normally produce erythropoietin, a hormone that stimulates red blood cell production. Some cats with CKD develop anemia and may benefit from treatment with darbepoetin.
- Subcutaneous (SQ) fluids. In the later stages of CKD, cats cannot drink enough to maintain healthy hydration. SQ fluids are well tolerated by cats and can improve their quality of life.
- Intravenous (IV) fluids: In advanced stages of kidney disease, high doses of IV fluids may be given to “flush out” the kidneys and bloodstream. This process, called diuresis, may help improve kidney function by removing accumulated toxins.
What is the prognosis for a cat with CKD?
Unfortunately, once the kidneys are damaged, they have minimal ability to recover. However, with proper management, most CKD cases progress very slowly. Your cat may have several years of quality, active life with treatment.