How Kidneys Work
The kidneys are a pair of organs inside the abdomen or belly that are part of the urinary tract (also known as the urogenital system). They filter toxins, waste, and extra water from the body via the bloodstream. The filtered water and waste gets transported to the bladder as urine via tubes called ureters. Kidneys also help sustain the electrolyte balance within the body, stimulate red blood cell production, and control blood pressure. Thus, when the kidneys aren’t working normally, many other body systems and organs are affected, including the heart and brain.
Kidney disease is classified in a few ways. Causes of failure, treatment, and outcome differ a bit between each classification form. Most commonly, kidney disease is classified as either acute kidney failure (also called acute kidney injury/AKI, acute renal failure/ARF) or chronic kidney failure (also called chronic kidney disease/CKD, chronic renal disease, chronic renal failure/CRF).
Causes of chronic kidney failure include birth defects or congenital diseases, viral infections (e.g. feline leukemia virus [FeLV], feline immunodeficiency virus [FIV], FIP), polycystic kidney disease, kidney cancer (i.e. renal neoplasia), kidney infections, elevated calcium (i.e. hypercalcemia), renal dysplasia, kidney stones (i.e. nephroliths or renoliths), blocked urine movement or flow (e.g. partial or treated urinary tract obstruction), immune system dysfunction, poor blood flow to the kidneys/ischemia, and certain medications (e.g. NSAIDs, certain antibiotics). Acute kidney failure can also lead to chronic kidney failure. In many cases, the cause of chronic kidney failure is not known.
The Path of Kidney Failure
Chronic kidney failure develops more slowly than acute kidney failure. At first, the kidneys try to make up for the damage by increasing the filtering ability of the healthy parts of the kidney. Over time, this causes damage to the healthy kidneys and they also lose the ability to filter properly. Proteins such as albumin, which help control the amount of fluid in the blood and support other body functions, enter the urine. Excessive amounts of certain electrolytes (e.g. potassium) and water are also lost in the urine, leading to chronic/constant dehydration and electrolyte-related issues (e.g. muscle weakness). Increased blood pressure (i.e. hypertension) may occur. Gastrointestinal (GI) issues such as ulcers are common because the kidneys can’t filter out toxins (e.g. uremia). Excess phosphorus is also normally removed by the kidneys but tends to build up with chronic kidney failure. This can lead to further kidney damage. The kidneys also make the hormone erythropoietin, which is in charge of stimulating red blood cell production. In chronic kidney failure, the kidneys don’t work well enough to make this hormone, so anemia (i.e. low red blood cells in the bloodstream) is also common.
Symptoms and Identification
Cats in chronic kidney failure may not show any symptoms at first, or the symptoms may be very subtle. Drinking and urinating a lot, especially when urine is very dilute or clear, are the most common symptoms. Weight loss, poor appetite, throwing up, and bad breath may be noted as well. Depending on what has caused the kidneys to fail, other symptoms may be present, such as straining to urinate or loose stool/diarrhea.
Bloodwork and urinalysis are commonly performed to diagnose kidney failure. With chronic kidney failure, checking blood protein levels, red blood cell percentage, and kidney values will help determine if too much protein is being lost in the urine (resulting in low blood protein), if the kidney disease has caused anemia, or if the kidneys are not effectively removing toxic substances from the body and/or removing too much water. Other abnormal lab values may suggest what caused the kidney disease (e.g. toxin, infection). Urinalysis will show if the kidneys can concentrate the urine correctly (meaning that they are not removing too much water from the body), if protein is being lost in the urine, and if other problems are occurring in the urinary tract such as infection or kidney/bladder stones. Blood pressure, x-rays, and abdominal ultrasound may also be performed to assess the severity of disease, get an idea of how the kidneys look, and to check for potential causes.
International Renal Interest Society (IRIS) offers staging methods to help monitor and treat patients in chronic kidney failure. Stages 1-4 are based on how well the kidneys can concentrate urine and filter toxins out of the blood. Laboratory values (e.g. SDMA, creatine) and urinalysis are used as criteria to move from one stage to the next, with stage 1 indicating mild kidney failure (i.e. minimal laboratory value changes) and 4 being severe (i.e. major changes). Substaging also helps determine failure severity and treatment needs. Substaging in chronic failure is determined by how much protein is in the urine and if high blood pressure is present.
Chronic kidney failure is the most common form of kidney disease, affecting up to 3% of all cats. Chronic kidney failure is more common in older cats.
Cat breeds that may be at a higher risk for chronic failure than other breeds:
Chronic kidney failure cannot be cured, and treatments will be needed for the remainder of the pet’s life. Diet change can be very helpful. Prescription diets low in phosphorus, sodium, and protein as well as high in fiber, calories, and omega 3 fatty acids have been shown to decrease the episodes of high levels of uremia (i.e. uremic crisis), a toxin which builds up during renal failure. Such diets have also been demonstrated to prolong the lifespan of cats with chronic renal failure. Canned diets may be better than dry diets because they increase fluid intake, which helps combat dehydration.
Subcutaneous (SQ) or intravenous (IV) fluid administration may be needed weekly to every few days, depending on how severe the chronic kidney failure is. Fluids help fight chronic dehydration and help flush the kidneys to remove bodily toxins. While scientific studies have not proven that daily or weekly fluid therapy increases lifespan, it does make pets in renal failure feel better. Most cats eat better and are more active after treatments.
Medication to decrease blood phosphorus levels may be given if phosphorus gets too high. Treatment for anemia may also be needed. This can include blood transfusions or giving a medication to simulate erythropoietin. Pets with high blood pressure will need hypertension medication (e.g. benazepril, amlodipine). Some of these medications may be helpful for decreasing protein in the urine (e.g. benazepril) as well. Appetite stimulants and GI-protective medications may also be needed in cats with ulcers or toxic levels of uremia.
Renal Replacement Therapy
Kidney dialysis (i.e. both hemodialysis and peritoneal dialysis) and/or renal transplant, more commonly done in people, are rarely done in animals. These procedures are usually only available at specialized veterinary institutions or facilities.
Veterinary cost varies quite a bit depending on acute vs chronic kidney failure, the underlying cause, and how the pet responds. Initial identification tests for diagnosis usually range from $200-750. Long-term management of chronic kidney failure may range from $100-500 a month, depending on what medications are prescribed and how often fluid therapy is needed.
Unfortunately, little can be done to prevent kidney failure. Avoid exposing your cat to toxic substances. Take him or her in for yearly check ups. Monitor for changes in drinking and urinating habits to ensure treatment can be started as soon as your cat becomes sick. Always call your vet with questions/concerns.
Polzin DJ, Ettinger SJ: Chronic Kidney Disease. Textbook of Veterinary Internal Medicine, 7th ed. St. Louis, Saunders Elsevier 2010 pp. 1990-2021.
Bartges JW: Chronic kidney disease in dogs and cats. Vet Clin North Am Small Anim Pract 2012 Vol 42 (4) pp. 669-692.
Korman R: Chronic Kidney Disease (CKD) - Aetiology, Diagnosis and Staging. International Society of Feline Medicine Asia Pacific Congress, 2014.
IRIS Staging of CKD. Updated 2019. Accessed on September 19, 2020.
Mitani S, Yabuki A, Taniguchi K, et al: Association between the intrarenal renin-angiotensin system and renal injury in chronic kidney disease of dogs and cats. J Vet Med Sci 2013 Vol 75 (2) pp. 127-133.
White JD, Stevenson M, Malik R, et al: Urinary tract infections in cats with chronic kidney disease. J Feline Med Surg 2013 Vol 15 (6) pp. 459-465.
Adams LG: Treatment of Chronic Kidney Disease: An Evidence-Based Medicine Approach. BSAVA Congress, 2011.
Fritsch DA, Jewell: Acceptance and effects of a therapeutic renal food in pet cats with chronic kidney disease. Vet Rec Open 2015 Vol 2 (2) pp. 1-7.
Lee YJ, Chan JP-W, Hsu KW: Prognostic factors and a prognostic index for cats with acute kidney injury. J Vet Intern Med 2012 Vol 26 (3) pp. 500-505.
Boyd LM, Langston C, Thompson K, et al: Survival in cats with naturally occurring chronic kidney disease (2000-2002). J Vet Intern Med 2008 Vol 22 (5) pp. 1111-1117.