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March 4, 2021 – Chronic kidney disease (CKD) is one of the most common, if not the most common, diseases of older cats. Although less frequently found in dogs, it can be a serious problem in this species, too.

CKD in dogs and cats is a complicated problem and has been a major focus of veterinary research (especially in cats) for decades. It was Buddy, a dog with kidney disease, that prompted Dr. Mark Morris Sr. to create the first prescription diet – you could say that the Foundation has been interested in CKD for a very long time!

The kidney

The kidney is made up of thousands of functional units called nephrons. A nephron is a complex structure, but its main functions boil down to:

  • Filtering substances (both harmful and normal) out of the blood
  • Regulating, via reabsorption and excretion, important molecules such as electrolytes and water
  • Forming urine, the end product of all these other processes
  • Vitamin D metabolism
  • Blood pressure regulation
  • Red blood cell production

Keeping these functions in mind helps when it comes to understanding diagnostic testing and therapy for kidney disease.

Chronic kidney disease – the basics

CKD is defined as abnormal function or structure of the kidneys that lasts for more than three months. In reality, it’s not easy to pinpoint the precise moment that CKD begins, but once started, a relentless decrease in kidney function is set in motion. This decline can take anywhere from months to years to progress.

Because cats and dogs have two kidneys, normal function and health can be maintained even if there is some damage to a single kidney. While this redundancy is helpful in the short term, it means current testing methods don’t detect chronic kidney problems until a lot of damage has already happened. Even then, if the disease has progressed slowly, many cats and dogs might not have any signs of kidney problems at all!

Stages of CKD

For many years, there were inconsistencies in the terminology and definitions surrounding CKD. This made it tough for pet owners and veterinarians to make apples-to-apples comparisons between studies.

In 1998, a group of veterinary kidney experts decided to form a society that would provide standards to facilitate communication among veterinarians around the world. In addition, they wanted to provide the latest recommendations on managing kidney disease in dogs and cats based on the best available science. Out of this collaboration, the International Renal Interest Society (IRIS) was created.

IRIS divides CKD into four stages (and substages) based on four criteria:

  • Blood creatinine levels
  • Blood symmetric dimethylarginine (SDMA) levels
  • Blood pressure measurement
  • Urine protein levels

A cat or dog is assigned to a stage and substage based on these measurements. There are specific treatment recommendations made for each stage. A cat or dog can change stages based on their response to treatment, although typically patients will progress to higher stages as their kidney function worsens.

The IRIS website has detailed information for both pet owners and veterinarians and is definitely worth reading, especially by owners of pets with CKD.

Diagnosis of CKD

Diagnosis of CKD relies on a combination of clinical signs and laboratory tests. Unlike some diseases, laboratory tests can be very helpful in the diagnosis of this disease, especially when there are no clinical signs. Often, CKD is diagnosed during routine annual bloodwork screens in older individuals.

Clinical signs of CKD, when present, include:

  • Increased thirst and urination
  • Decreased appetite
  • Vomiting
  • Bad breath
  • Lethargy

Laboratory analysis of blood and urine, and accurate blood pressure, are crucial pieces of the diagnostic puzzle. As noted earlier, these values are used to determine IRIS stage, which in turn guides therapy.

Occasionally, other tests are used to help determine the cause of decreased kidney function and help rule in or out CKD. Additional tests can include abdominal ultrasound, urine culture for bacteria, or tests for other diseases that can affect the kidneys such as leptospirosis or Lyme disease.

Treatment of CKD

CKD treatment goals are similar for both dogs and cats, and these fall into several broad categories:

  • Diet changes to slow progression of disease (if possible)
  • Maintaining hydration
  • Maintaining appetite and providing nutritional support
  • Correcting low red blood cell count (anemia)
  • Lowering phosphorus
  • Treating high blood pressure

Dietary management remains the cornerstone of therapy for CKD. Although research continues fine tuning diets for dogs or cats at each stage of CKD, there is solid evidence regarding general diet recommendations. These include:

  • Restricting phosphorus and sodium intake
  • Feeding a diet with a moderate amount of high-quality protein
  • Increasing omega-3 fatty acid intake
  • Increasing potassium in the diet for cats
  • Adding antioxidants and fiber

Diet changes are most effective when a dog or cat is in IRIS Stage 2 or 3 and is still eating well.

Maintaining hydration is important, since pets with CKD cannot reabsorb water well and are susceptible to rapid dehydration. Access to fresh, clean water is crucial, and occasionally fluid therapy using subcutaneous fluid administration is necessary.

Other medications to correct phosphorus imbalance, address anemia and reduce blood pressure may be necessary as well.

It’s important for owners to work with their veterinarians closely when it comes to treatment of CKD. Your veterinarian can guide you on what treatments are best for your dog or cat and set up a schedule to monitor response to therapy. These treatments can vary over time as a patient’s IRIS stage changes or other diseases are diagnosed that can impact CKD therapy.

Morris Animal Foundation has been studying CKD since the Foundation was established 73 years ago. We have several additional resources available for readers who would like to learn more about this disease. Take a look at our CKD research portfolio and check out ways you can help us find solutions for dogs and cats suffering from CKD – working together, we can help pets live happier, healthier lives!

Fresh Scoop podcast on CKD in cats

AnimalNEWS 101 webinar on CKD in cats