Gary Norsworthy, DVM, Dipl. ABVP (Feline), owner of Alamo Feline Health Center in San Antonio, believes veterinarians should be careful when using the term “kidney failure” in talking to cat owners.
To determine kidney function, creatinine and BUN (blood urea nitrogen) tests are conducted. Kidney failure occurs in a dog in which the creatinine value from blood tests is over 2.5 mg/dl, giving a dog a month or two to live.
A creatinine number over 2.4 signals kidney trouble for a cat, yet actual kidney failure for a cat doesn’t start until that number reaches 5.0 or 5.5 mg/dl, Dr. Norsworthy said.
Poor word choice can come into play when a veterinarian gets blood test results back with a creatinine value over 2.4 for a cat, he said.
“Many cats are diagnosed with kidney failure that don’t have failure,” he said.
Norsworthy said that in such cases he advises practitioners to use the term “kidney insufficiency,” a phrase he considers more accurate to describe cats in this range.
“That’s an important distinction,” he said. “If you use the term ‘failure,’ owners wonder if their cat’s about to die. So cats often get euthanized when they shouldn’t.”
With proper treatment, Norsworthy said, cats with kidney insufficiency frequently live for one to three years before kidney failure and death, and they can live a fairly normal life.
When Norsworthy treats cats with kidney inefficiency he pays close attention to two electrolytes: the phosphorous and the potassium levels.
The phosphorous level can get too high, so it must be brought down, while the potassium can get too low and must be brought up, he said.
“Managing the electrolytes is part of the treatment,” Norsworthy said.
Christopher G. Byers, DVM, Dipl. American College of Veterinary Emergency and Critical Care, Dipl. ACVIM (small animal internal medicine), believes every veterinarian should be familiar with the staging system for chronic kidney disease developed by the International Renal Interest Society.
IRIS staging is undertaken following the diagnosis of chronic kidney disease to facilitate appropriate treatment and monitoring of the patient, and is based initially on fasting blood creatinine assessed on at least two occasions in a stable patient.
The patient is then substaged based on proteinuria and systemic blood pressure, according to IRIS guidelines.
“Use of the IRIS staging system yields prognostic information and helps identify consequences of CKD for which veterinarians can prescribe interventions,” said Dr. Byers, a faculty criticalist/internist at Midwest Veterinary Specialty Hospital in Omaha.
“Simply stated, universal application of this staging system could enhance our understanding of CKD in dogs and cats and allow veterinarians to identify optimal therapies.”
Byers said he would like veterinarians to appreciate the incidence of renal secondary hyperparathyroidism and the renoprotective role of calcitriol therapy in patients with chronic kidney disease.
He said a previous study (Polzin et al, J Vet Intern Med, 2005) confirmed that calcitriol prescribed to treat renal secondary hyperparathyroidism caused a 68 percent reduction in mortality.
“Extrapolation from dogs to cats suggests the benefits should be similar in cats with CKD,” Byers said.
A common oversight by veterinarians that Byers sees is failure to obtain concurrent urine samples when evaluating blood renal values.
“If a clinician wants to satisfactorily assess renal function, both blood and urine must be analyzed,” he said. “Failure to properly perform a complete urinalysis can lead to misdiagnoses and inadequate therapeutic interventions.”
Cats Living Longer
Cats are living longer today – and that has implications where chronic kidney disease is concerned, the experts said.
In 1983, 26 percent of cats were older than age 6, and by 1996 47 percent of cats were 6 or older, according to surveys from the American Veterinary Medical Association. A 1999 survey of primary care practices in the U.S. showed that 20 percent of cats were older age 10 years and 5 percent were older than 15.
Byers pointed to these statistics to make his case that the cat population has grown in age due to better veterinary care, among other factors.
“The cause of this increased longevity is unquestionably multi-faceted, and I suspect increased awareness by owners of advanced medical and surgical interventions available for their pets, as well as the phenomenal veterinary care provided to these pets are the major contributors these statistics,” Byers said.
It is because cats are living longer – and because they can continue to live a normal life if diagnosed early and treated property – that Norsworthy recommends that veterinarians actively look for cats entering the kidney insufficiency stage by ordering a senior blood panel for their cat patients age 10 and up.
“That will allow you to find it early and treat them,” he said.
Since chronic kidney disease is common in elderly cats, the importance of screening cannot be overstated, said Jessica Quimby, DVM, Ph.D., a faculty member in small animal internal medicine at Colorado State University Veterinary Teaching Hospital.
“Early diagnosis has been associated with longer survival,” said Dr. Quimby, a member of the American Association of Feline Practitioners.
“Just knowing that a cat has CKD will encourage a higher level of monitoring at home, more frequent vet visits, more care with procedures, drugs and anesthesia. Regular monitoring for metabolic complications of disease will allow them to be addressed in a timely manner with the goal of slowing disease progression.”
Quimby has seen a higher incidence of chronic kidney disease in cats in recent years, and she attributes this to better care and better medicine.
“We do feel that cats are living longer than they did 20 years ago, and I’d like to think that we are better at diagnosing them early and helping manage the disease rather than seeing them in late stage disease in a uremic crisis,” she said.
A changing view of the best diet is a key development in the treatment of chronic kidney insufficiency, Nortsworthy said.
In the past, the approach was a low-protein diet. Now the practice is to put such a cat on a high-protein diet, he said.
There are several reasons for this switch in thinking, particularly to keep the cat from losing too much weight and muscle. Muscle wasting is a common problem in senior cats, Norsworthy noted. Their spines and hips become very prominent because they have lost muscle mass. This occurs due to protein deprivation.
“The low-protein diet really hasn’t done the good that we thought it was doing,” Norsworthy said, adding that its benefits to kidney function “are minimal to nil” and that many older cats on a low-protein diet will begin to lose muscle and get thin.
Despite this change in thinking, many manufacturers continue to make low-protein diets that are officially labeled for the kidney disease, he said.
“I don’t even use those official kidney diets anymore,” Norsworthy said. Instead he recommends foods made for diabetes patients because they are low in carbohydrates, which is in excess amounts in many cat foods, and the food makers have replaced the carbs with mostly proteins.
Norsworthy noted that creatinine is artificially lowered when a cat loses a lot of weight, and muscle mass is needed to make creatinine.
“In a very thin cat, the creatinine will not be a true reflection of the kidney function,” he said.
That means the creatinine measurement is not reliable in a thin cat, and on the other hand the BUN measurement is falsely elevated in a cat that’s dehydrated. “Therefore, you have to consider body condition and hydration status when interpreting creatinine and BUN values,” he said.
High protein diets will elevate the BUN measurement, but that doesn’t mean the kidney function is down, he said. “It just means the cat’s on a high-protein diet.”
A picky appetite is one of the most common concerns Quimby hears about patients with chronic kidney disease
“Appetite should be actively addressed, as poor body condition is linked to a poor prognosis,” she said.
Treating complications of the disease, like hypertension, dehydration and anemia, will help maintain appetite, Quimby said, but feeding tubes, appetite stimulants and anti-nausea medications should be considered to manage nutrition.
Byers is excited by a potential breakthrough in diagnosing chronic kidney disease may come from any of the various studies that have confirmed that symmetric dimethylarginine – a byproduct of protein methylation that is eliminated by the kidneys – is a precise biomarker for calculating estimated glomerular filtration rate in humans, and is more sensitive than serum creatinine for assessing renal dysfunction.
Studies have shown that measuring SDMA levels allowed earlier detection of chronic kidney disease in cats compared with serum creatinine, Byers said.
“These results are encouraging, as early recognition of CKD will empower veterinarians with invaluable information about initiating renoprotective therapies that could slow CKD progression,” Byers said.
Quimby believes there haven’t been enough breakthroughs in treating or understanding more about this disease.
“One of the most discouraging things about CKD is that despite its prevalence, we still have very little idea what causes it or why it is so common in elderly cats,” Quimby said.
However, she is encouraged by the emergence of recent studies focusing on exploring etiology of the disease and possible treatment options.
“A new focus of several research groups has been to better understand the pathophysiology of feline chronic kidney disease to direct us in the development of novel therapies,” Quimby said. “Although this information is not currently available, it is a very important area and provides hope for the future.”