Chronic kidney disease (CKD) in dogs is generally progressive, meaning that once it begins, there’s typically no cure. With early intervention, however, it can be possible to slow the progression of the disease.
To help veterinarians provide the best care for dogs and cats with CKD, the International Renal Interest Society (IRIS) developed a system to “stage” the disease. It’s not another method for diagnosing CKD, but a way, after diagnosis, to tailor treatment, monitor disease progression and assess patient prognosis. Identifying where in the course of the disease’s progression a pet is, especially when in the early stages, helps the staging process work more effectively.
Early diagnosis is difficult
The kidneys are primarily responsible for filtering out waste products from the blood. As the kidneys begin to fail, they can often compensate, so dogs usually don’t show any clinical signs such as increased thirst and urination in the early stages of the disease.
It’s not until waste products, specifically creatinine (from muscle metabolism) and blood urea nitrogen (or BUN, a liver byproduct) begin to build up in the blood that abnormalities may surface on traditional screening tests. When the urine-specific gravity, which measures the kidneys’ ability to concentrate urine, is also abnormal, a diagnosis of kidney failure is made.
The trouble is that by the time these traditional tests catch kidney disease, the kidneys may have already lost 75 percent of their function.
A relatively new test detects symmetric dimethylarginine (SDMA) and may identify kidney disease earlier, since this biological marker rises in the blood earlier than creatinine — on average, the diagnosis can be made when there’s been a 40 percent loss of kidney function. In dogs, that could mean, on average, about 9.5 months earlier than with traditional tests. Once a diagnosis of CKD has been made, IRIS staging can be done.
The IRIS system categorizes stable, hydrated dogs with CKD into four stages, based on blood levels of creatinine, SMDA or, preferably, both:
- Stage I (pre-failure): Dogs typically have normal blood creatinine or normal/slightly elevated SDMA. Kidneys may appear abnormal on X-ray or when veterinarians feel or “palate” the kidneys on examination. Dogs generally don’t show clinical signs.
- Stage II (mild failure): Creatinine is normal or mildly increased and SDMA is mildly increased. Clinical signs may be absent or mild.
- Stage III (moderate failure): Creatinine and SDMA are moderately elevated. Signs may be absent or obvious.
- Stage IV (severe failure): Creatinine and SDMA are extremely elevated. Dogs show signs of illness at this point.
Within each stage, dogs are also substaged, based on tests that measure protein in the urine (proteinuria) and increased blood pressure, two CKD complications.
The IRIS staging system also includes treatment recommendations aimed at preserving kidney function (and slowing disease progression) while improving quality of life for the pet. With early diagnosis, veterinarians can intervene at stage I or II, when treatments can be more effective at slowing disease progression. However, many dogs may not be diagnosed until they have already reached the latter stages of CKD. At that point, the treatment emphasis is more on helping reduce clinical signs and improving pet comfort.
No matter how far the disease has progressed, with the IRIS system, your veterinarian can monitor response to treatment and revise the dog’s staging and treatment as needed, and provide a better quality of life for as long as possible.