Cats’ kidneys are vital organs that filter waste and toxins from the blood, help manage blood pressure, and produce several necessary enzymes and hormones. Research shows that during a feline lifetime, one in three cats will develop chronic kidney disease — a leading cause of death in cats age seven and older. Cats as well as their kidneys share complicated natures.
In cats, early detection of any disease is, well, a bear. While cats are fierce little predators, they are also prey to larger carnivores. A visibly sick animal is as good as a coyote’s main course. As a survival strategy, cats conceal any sign of illness from potential predators (and you) as long as possible. Whether we’re looking at kidney decline, heart failure, or other conditions, even the most observant owner might not notice symptoms until a cat is already is critically ill.
Several years ago, 13-year-old Nermal appeared to be healthy and happy, but one day his owner realized the Maine Coon mix wasn’t acting like himself. He had no specific symptoms, just the impossible-to-describe “ain’t doin’ right.” Nermal’s veterinarian said he was fine, but the cat was far from fine. A few months later, Nermal suddenly dropped three pounds. His creatinine blood levels showed he was in end-stage kidney failure.
In cats such as Nermal who have chronic renal disease failure, the kidneys are scarred, and their filtering ability irreversibly compromised. Nermal’s story didn’t have a happy ending because his kidney disease was discovered too late.
Kidney failure is tricky. While loss of the kidneys’ ability to filter toxins can be the result of a stand-alone condition, it can also be caused by a disease that has not been found or diagnosed in a particular cat.
According to Dr. Cynthia Rigoni, owner of All Cats Veterinary Clinic in Houston, infection as well as diseases of other organs can affect the kidneys: hyperthyroidism, heart disease, pancreatitis, and even dental disease. These processes and the resulting kidney decline can often be managed if caught early enough.
Cardiac or thyroid disease can increase or decrease blood pressure, which affects blood flow to the kidneys. Other conditions attack the kidneys, scarring the filtering tissue called nephrons. Once scarred, nephrons can’t be repaired. Kidney function deteriorates, leading to renal failure and eventually death.
Until a few months ago, vets and cat owners could respond to hard-to-detect illnesses only in the later stages, when the cat could no longer hide his symptoms, or creatinine values changed in bloodwork. Creatinine screening, used to diagnose Nermal’s kidney failure, won’t reveal elevated quantities of creatinine (chemical waste generated by muscle tissue) until the cat has already suffered a 75 percent kidney-function loss. Also, creatinine values are affected by body mass, not kidney function, so a healthy bulky bulldog will produce higher levels of creatinine than a healthy skinny Siamese.
Fortunately, Idexx Reference Laboratories in recent months made available to U.S. vets the symmetric dimethylarginine blood screen, a test for kidney disease in cats and dogs. Also called SDMA, symmetric dimethylarginine is a small protein released into the feline bloodstream and eliminated by the kidneys. It more accurately reflects the kidney’s true filtering ability. When kidney function declines because of disease or injury, SDMA in the blood increases. SDMA appears in the blood an average of 17 months earlier (when there is only 25 percent to 40 percent kidney loss) than creatinine. By the time creatinine increases, 75 percent of the kidney is lost. Idexx has added this proprietary screening to all routine blood panels sent to Idexx labs at no additional charge.
While the advantage to early diagnosis is obvious, another advantage of SDMA is alerting the vet to the possible presence of other medical conditions.
The SDMA test will not tell you the cause of the kidney decline, but it will alert your vet to further investigate the underlying cause, such as hidden infection, cardiac disease, pancreatitis, lymphoma, kidney stones, dental disease, and cancers. After conducting a physical exam and seeing the results of bloodwork, your vet might order a urine analysis or urine culture, a more comprehensive blood panel, X-rays, or ultrasound.
Rigoni encourages her clients to initially order the comprehensive blood panel that includes not only SDMA but also a pancreatitis screen. She often finds multiple simultaneous conditions contributing to kidney deterioration. If the owner opts for a more limited panel and the SDMA is elevated, Rigoni goes hunting for other undetected disease. Rigoni says this earlier detection of kidney disease buys her “time to hopefully fix the problem.”
Says Dr. Roberta Relford, vice president and chief medical officer at Idexx Reference Laboratories, “If you wait until end-stage disease, when the kidney is scarred and shrunken, it’s too late to discover the cause.”
She says Idexx has seen several cases where an animal was not obviously sick, and the creatinine was normal, but the SDMA was elevated. The animals were later found to have kidney stones, a condition that is often treatable.
Unlike bladder stones, which irritate the bladder and cause observable symptoms, small kidney stones don’t produce obvious signs. Inevitably, stones grow so large they affect kidney function. Earlier detection allows vets to treat stones before permanent damage occurs.
SDMA screening allows pet owners to take early action on a condition rather than reacting to a full-blown crisis.
Once a cat owner is aware of kidney disease, he or she can provide more sources of hydration such as water fountains and adding water to food. A vet can take steps to preserve the cat’s kidney function by switching to kidney-friendly medications and diet, Relford says.
SDMA is available only at Idexx laboratories. Because this is a proprietary screen, neither in-house blood diagnostics nor other labs offer it. Relford says if your cat needs bloodwork, ask your veterinarian for an SDMA test.
“Every vet has access to this test,” she says. “Even if your vet doesn’t normally use an Idexx reference laboratory, she can still send the specimen to Idexx,”
Idexx recommends getting an SDMA baseline when the cat is between two and four years old, so your vet can monitor the rate of kidney decline as your cat ages.
About the author: Dusty Rainbolt, ACCBC, is the past president of the Cat Writers’ Association, editor-in-chief of AdoptAShelter.com and an associate certified member of the International Association of Animal Behavior Consultants. She’s the award-winning author of ten fiction and non-fiction books including her most recent paranormal mystery, Death Under the Crescent Moon.