Chronic Kidney Disease Diagnosis in Dogs and Cats
The kidneys shrink with chronic disease until they no longer properly function
Chronic kidney disease (CKD) is a common disease in dogs and cats. The prevalence of CKD in cats increases as pets age with up to 30% of geriatric cats and 10% of geriatric dogs being affected. Although CKD is a progressive disease, early diagnosis and management may modify the rate of progression and improve patient quality of life.
The kidney’s function is to filter the blood numerous times daily. The kidneys preserve body water from getting into the urine and they excrete toxins, minerals, and hormones. The kidneys can become damaged from chronic infections, like dental disease, toxins in the blood from poisonings or ingestions, certain infectious diseases, stones, and many other conditions including heart disease.When the kidneys are not working properly, there is more water in the urine and it is much less concentrated. When dogs excrete more water, they have to drink more to replace it. In dogs, drinking excessive water and urinating more frequently may be the first indication of CKD. Since cats can maintain their ability to concentrate urine even when the kidneys are damaged, they do not show as much excess water consumption. However, as urine concentrating ability is lost later as the disease progresses, cat owners are more likely to recognize increased thirst.
Dogs and cats in the later stages of kidney disease often show nonspecific signs, including poor body condition, weight loss, decreased appetite, lethargy and dehydration. Intermittent vomiting and diarrhea due to ulcers in the stomach and intestines may show up when toxins and hormone levels increase in the blood because the kidneys cannot get rid of them. Urinary tract infections are more common as the urine becomes more dilute. Bacteria do not thrive in concentrated urine, but when the urine is dilute, they have a better chance of causing infection.When we examine the older patients with kidney disease, we often see poor body condition, poor hair coat, dehydration and shrunken kidneys. Oral examination may reveal pale mucous membranes from anemia, mouth ulcers, badly infected gums and/or bad breath.
A diagnosis of CKD is typically straight forward once the disease is in its later stages and there is clinical suspicion based on history and physical examination findings. Usually these chronic kidney disease signs do not typically develop until approximately 75% of kidney function is lost. When we do blood tests, increases in the kidney indicators are evident on biochemical profile (BUN, Creatinine, and Phosphorus). When we check the urine, we can determine if there is loss of urine concentrating ability and loss of proteins in the urine. By then there is not too much we can do to intervene and help these patients.
There is a new test called the SDMA test we now have that can detect damage to the kidneys much earlier than we could previously. The SDMA test can detect kidney damage as soon as 40% of the function of the kidneys is lost. We can intervene by changing their diet to a very low protein diet and by changing some medications that can affect the kidneys.
SDMA is a product of the breakdown of dietary proteins. The amino acid arginine, which is released into the circulation during protein degradation, is excreted almost exclusively by the kidneys. So when the kidneys cannot get rid of SDMA, it increases in the blood well before any of the other test values increase. Knowing that there is early kidney damage before symptoms show up can give your dogs and cats a longer healthier life.We recommend this test on all of our 7 years and older dog and cat patients. We also use this test on younger patients when we see the biochemical tests for the kidneys increase in younger animals. These increases may be from some non-kidney related disease and the SDMA can help us differentiate true kidney disease from something else causing the increases.