What do kidneys do?
The kidneys have many functions. They principally act to remove waste products from the bloodstream, regulate the levels of certain essential minerals such as potassium and sodium, conserve water, and produce urine.
What is chronic kidney disease?
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.
Chronic kidney disease used to be called chronic kidney failure. It is mainly a problem in mature and senior cats (seven years and older), affecting an estimated 30-40% of cats over 10 years and 81% of cats over 15 years. Only about 10% of the cases occur in cats less than three years old.
What are the clinical signs of chronic kidney disease?
Early signs of disease, such as weight loss and poor coat quality, are often dismissed as normal aging changes. In the initial stages of kidney failure, the kidneys cope with their inability to efficiently remove waste products by excreting them at a lower concentration over a larger volume (in other words, by producing a larger amount of more dilute urine). Cats will often drink more to compensate for this increased rate of body water loss. This is known as compensated renal failure. After approximately two-thirds of the kidney tissues have failed, there is a rapid rise in waste products in the bloodstream and an apparent sudden onset of severe disease.
"After approximately two-thirds of the kidney tissues have failed, there is a rapid rise in waste products in the bloodstream and an apparent sudden onset of severe disease."
What causes chronic kidney disease?
CKD is the end stage of various disease processes rather than a specific disease in its own right. Diseases or conditions that can eventually lead to CKD include:
1. Congenital (born with) malformations of the kidneys, such as polycystic kidney disease in long-haired cats (see the handout "Polycystic Kidney Disease in Cats" for more information)
2. Pyelonephritis (bacterial kidney infections—see the handout “Pyelonephritis in Cats” for more information)
3. Glomerulonephritis (inflammation and damage to the kidney's filtration membrane—see the handout "Glomerulonephritis in Cats" for more information")
4. Neoplasia (various tumors of the kidney), most commonly lymphosarcoma
5. Amyloidosis (build-up of an unusual protein in the kidney that prevents it from functioning normally—see the handout "Amyloidosis in Cats" for more information)
6. Viral infections, such as feline leukemia virus (FeLV) and feline infectious peritonitis virus (FIP)—see the handouts “Feline Leukemia Virus Disease Complex” and “Feline Infectious Peritonitis” for more information
7. Kidney stones or ureteral stones
"CKD is the end stage of various disease processes rather than a specific disease in its own right."
How is the disease diagnosed?
Renal disease is usually diagnosed by looking at the level of two biochemical by-products in the bloodstream, blood urea nitrogen (BUN) and creatinine, in conjunction with the urine specific gravity (USpG). Proteinuria (excess protein in the urine) is another indicator of CKD. Tests to measure the blood levels of other substances such as proteins, potassium, phosphorus, and calcium, as well as the red and white blood cell counts, are essential to determine the extent of kidney failure and the best course of treatment.
Could the disease have been diagnosed earlier?
Until recently, early diagnosis of chronic renal failure was challenging. Neither clinical signs of renal failure nor rises in BUN and creatinine are evident until significant loss of kidney function has occurred. A newer blood test to assess levels of SDMA (a naturally occurring biological indicator for kidney function) has been used to determine if early renal failure is occurring. SDMA concentrations increase above the normal reference interval well before serum creatinine becomes elevated. This will help your veterinarian provide treatment for your cat at a much earlier stage in the disease.
How will my veterinarian determine the degree of kidney disease in my cat?
Your veterinarian will use the IRIS (The International Renal Interest Society) staging system. IRIS staging is based on serum creatinine levels, with sub-staging based on the presence of protein in the urine (as determined by a urine protein: creatinine ratio [UPC]) and measuring your cat’s blood pressure. This staging gives your veterinarian a better idea of how to proceed with treatment, monitor progress, and estimate your pet’s prognosis.
How does chronic kidney disease affect my cat?
Because the kidneys perform various functions, the clinical signs of CKD can be somewhat variable. The most common changes are weight loss, poor hair quality, halitosis (bad breath), and variable appetite, which may be associated with mouth ulcers, lethargy, and depression. Less common signs include increased drinking or urinating, vomiting, diarrhea, and anemia.
"The most common changes are weight loss, poor hair quality, halitosis (bad breath), and variable appetite..."
What treatments are available?
The treatment of CKD depends on the results of blood tests, and specific treatments aim to resolve specific abnormalities. 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 lower the level of waste products in the bloodstream. These can be prepared at home or are available ready prepared from your veterinary practice.
• Phosphate binders. Despite low phosphate in the diet, blood phosphorus levels remain above normal in some cats. Reducing blood phosphorus can have a significant effect on improving your cat's well-being and slowing disease progression. Oral phosphate binders such as aluminum hydroxide help to lower the amount of phosphorus absorbed through the gut wall.
• Antibiotics. Cats with CKD develop bladder infections more frequently, increasing the risk of kidney infections, so routine urine cultures are recommended for many patients.
• Potassium supplementation. Cats in renal failure tend to lose too much potassium in the urine. This leads to muscle weakness, stiffness, and poor hair quality. Low potassium levels may also contribute to the worsening of kidney failure.
• B Vitamins. When the failing kidneys cannot concentrate the urine, water-soluble vitamins like B12 become depleted, and affected cats need supplementation.
• Anti-emetics. For those cats experiencing vomiting, using anti-emetics (anti-vomiting medications) reduces nausea, thereby improving appetite.
• Blood-pressure lowering drugs. Many cats with kidney failure have high blood pressure, leading to further kidney damage. High blood pressure can be managed with medication.
• Medication to reduce proteinuria, another condition that can hasten the progression of CKD.
• Treatment for anemia. Kidneys initiate the production of red blood cells in the bone marrow. Many cats with CKD are anemic due to a lack of stimulation of the bone marrow. Newer drugs have been developed to help stimulate bone marrow production and may be prescribed for your cat.
• 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.
What is the life expectancy for a cat with chronic kidney disease?
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.