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).
Acute kidney failure is triggered by sudden injury to the kidneys that causes them to stop functioning properly. This malfunction leads to a rapid decline of the health of the kidneys themselves as well as the other body systems that the kidneys normally help maintain. While acute kidney failure is very serious, and a pet can become extremely ill, some pets can survive with proper treatment.
Common causes of acute kidney failure include infection (e.g. leptospirosis, feline infectious peritonitis [FIP]), decreased blood supply (i.e. ischemia), toxins, excessive blood loss, very low blood pressure, burns, liver failure, cancer, kidney infections (i.e. pyelonephritis), bee or snake venom, urinary tract obstruction, and sepsis (i.e. blood infection). The most common toxins in cats are lilies, ethylene glycol/antifreeze, certain antibiotics, and nonsteroidal anti-inflammatory drugs/NSAIDs (e.g. ibuprofen).
The Path of Kidney Failure
With acute kidney failure, kidney cells are damaged to the point that they cannot receive oxygen from red blood cells. They lose their ability to filter the blood properly, leading to loss of some electrolytes (e.g. potassium) and retention of others (e.g. phosphorus), which damages the kidney cells further. The filter portion of the kidneys gets clogged with damaged cells as well as proteins, which are normally too big to be filtered through the kidneys and into the urine. Inflammation from the damage causes further dysfunction, creating a destructive cycle. Severe dehydration can occur. At some point, this process is irreversible, although if the kidneys recover, they may be able to still function a little. In some cases, acute kidney failure patients recover initially, only to develop chronic kidney failure later. Unfortunately, about half of cats that develop acute kidney failure do not survive, and a quarter to half of survivors have permanent damage.
Symptoms and Identification
Bloodwork and urinalysis are commonly performed to diagnose kidney failure. In cases of acute kidney failure, bloodwork can show changes in the white blood cells, which fight infection and cause inflammation. Bloodwork laboratory values that show how the kidneys are functioning (e.g. BUN, creatinine, and SDMA) may be extremely elevated. Other lab values may indicate how the body is handling the disease and what may have caused it. 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 grading methods to help monitor and treat patients in acute kidney failure. Grades 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 grade to the next, with grade 1 indicating mild kidney failure (i.e. minimal laboratory value changes) and 4 being severe (i.e. major changes). Subgrading also helps determine failure severity and treatment needs. Subgrading in acute failure is mostly based on the kidneys’ ability to produce urine.
Acute kidney failure can happen in any age, gender, or breed of cat.
If treated early, cats in acute kidney failure may improve. Considerable treatment and intensive care are needed. Hospitalization with intravenous (IV) fluids and electrolytes, medications to help increase urine production (e.g. furosemide), antibiotics to combat infection, and other treatments to manage what caused the kidney failure are often needed. Hospitalization and intensive care usually take several days before any improvement is seen. Urinalysis and bloodwork will likely be rechecked many times to monitor the pet. Some veterinarians will refer patients to a specialty hospital that provides 24-hour care in order to best provide for the pet’s needs.
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 the underlying cause and how the pet responds. Initial identification tests for diagnosis usually range from $200-750. Hospitalization and intensive care for acute kidney failure can range from $750-3,000.
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.
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