Maine Coon-mix, Nermal, appeared to be healthy at the age of thirteen. His owner couldn’t put his finger on it, but the kitty “didn’t act right.” After an examination, the vet declared Nermal was fine; he was not fine. Three months later, the orange tabby dropped three pounds over a weekend. His creatinine blood levels were so high the vet said “they weren’t conducive to life.” Sadly, Nermal’s story didn’t have a happy ending.
Because kitties live at the lower end of the food chain, and at the top of the menu for more powerful predators, they don’t want to draw attention to a weakened condition. As a survival strategy, stoic Fluffy conceals signs of illness from potential predators (and from you) as long as possible. Whether it’s kidney disease, heart failure or other condition, even the most observant owner may not notice symptoms until Fluffy is already beyond help.
Kidney disease is complicated
According to Drew D. Weigner, DVM, ABVP owner of the Atlanta-area clinic The Cat Doctor, “There are many causes of kidney disease in cats, but the most common is an age-related decrease in kidney function. Most geriatric cats will have this to one degree or another.”
While the breakdown of the kidneys’ ability to filter toxins can be the result of aging, it can also be caused by undiagnosed disease processes. By the time CKD cats begin showing symptoms (increased water consumption, frequent peeing, weight loss, loss of appetite and occasional vomiting), the kidneys are usually scarred, and their filtering ability irreversibly compromised.
Until recently, creatinine screening was the primary blood test used to diagnose CKD. It was better than nothing, but not much. Elevated levels of creatinine (a chemical waste generated by muscle tissue) don’t appear in the blood until the cat has already suffered a 75 percent irreversible kidney function loss. Also, creatinine values are affected by an animal’s body mass, not just kidney function, so a healthy bulky bulldog will produce higher levels of creatinine than a healthy slender Siamese. Because of this, creatinine levels can miss kidney disease in skinny cats. Like so many other kitties, Nermal’s symptoms and elevated blood creatinine appeared only after it was too late to help him.
Fortunately, Symmetric dimethylarginine (SDMA), a new blood screen test for kidney disease in cats and dogs, is now available to vets in the U.S. by IDEXX Reference Laboratories. SDMA, a small protein released into the cat’s bloodstream and eliminated by the kidneys, more accurately reflects the kidney’s true filtering ability. When kidney function declines, SDMA in the blood increases. SDMA appears in the blood an average of 17 months earlier than creatinine. At that point, there has only been 25 to 40 percent kidney loss. IDEXX has added this proprietary blood screen to all routine blood panels sent to IDEXX labs at no additional charge.
While the advantage to early diagnosis of kidney failure is obvious, SDMA can also alert a kitty’s vet to the possibility of other medical conditions, also allowing for earlier treatment.
SDMA can’t tell a veterinarian the cause of the kidney decline, but it can alert her to the possibility of multiple simultaneous conditions contributing to kidney deterioration. The vet will likely investigate underlying causes such as: hidden infection, cardiac disease, pancreatitis, kidney stones, dental disease, lymphoma and other cancers.
These conditions can 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. However, these conditions and the resulting kidney decline can often be managed if caught early enough.
“SDMA is quite specific for kidney disease, so an increase in SDMA is indicative of a decrease in kidney function,” Dr. Weigner says. “Since there are other diseases that can affect kidney function, other tests are run to look for these causes.”
Your vet may also order a urinalysis and/or urine culture, a more comprehensive blood panel, X-rays, or ultrasound.
“If you wait until end-stage disease, when the kidney is scarred and shrunken, it’s too late to discover the cause,” says Roberta Relford, DVM, MS PhD, DACVIM DACVP. Dr. Relford is the Vice President and Chief Medical Officer at IDEXX Reference Laboratories. She says IDEXX has seen several cases where an animal wasn’t obviously sick and the creatinine level was normal, but the SDMA was elevated indicating kidney disease was present. These cases were later found to have infections, tumors, kidney cysts, and a wide variety of kidney disorders. A few of these pets were eventually diagnosed with kidney stones. 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 you to treat stones before permanent damage occurs. So early detection is important to the healthy of your kitty.
SDMA screening allows you to be proactive about the health of your kitty rather than reacting to a full blown crisis. Once you’re aware of your cat’s kidney disease, you can offer more enticing sources of hydration such as adding water to food and setting up water fountains. Your vet can also take steps to preserve renal function by switching to kidney-friendly medications and diet.
SDMA is only available at an IDEXX Reference Lab. Because this is a proprietary screen, neither in-house blood diagnostics nor other labs offer SDMA. Dr. 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 as IDEXX has made accepting samples from any veterinarian an easy process.”
IDEXX recommends getting an SDMA baseline when the cat is between two and four, so your vet can monitor the rate of kidney decline as Fluffy ages.
“The beauty of SDMA testing is that it increases much earlier in kidney disease than traditional tests, so it allows a veterinarian to institute treatment much earlier in the course of the disease,” Dr. Weigner says. “This not only increases a patient’s longevity but also provides the opportunity to improve their quality of life.”
SDMA has been recognized by IRIS (the International Renal Interest Society) and has been incorporated into their kidney staging guidelines.