Written by Dr. Premnita Kalananthan, Veterinary Surgeon
What Is CKD (Chronic Kidney Disease)?
Dogs and cats have two kidneys, which are vital for maintaining life’s day-to-day processes. Many causes are associated with progressive loss of kidney function.
Unfortunately, once lost, the damage is irreversible. CKD, is one of the most prevalent diseases in older cats, affecting up to 40% of cats over the age of 10 and 80% of cats over the age of 15.
CKD means their kidneys gradually lose function over time, failing to filter waste, regulate electrolytes, and perform other vital jobs, leading to toxin buildup and serious health issues, common in older pets, with symptoms like increased thirst/urination, lethargy, and weight loss, requiring veterinary management.
Kidney failure often occurs when over 75% of the functional units (nephrons) stop working.
Symptoms often don’t appear until significant damage has occurred, making early detection crucial, especially in senior pets.
CKD has four stages based on the magnitude of decrease in kidney function.
Normal Function of Kidney
The kidney is an organ made up of hundreds of thousands of functional units called nephrons.
Each nephron is composed of a little filter called the glomerulus (plural, glomeruli) and a long passageway called the tubule.
All of the tubules eventually converge to form a collecting system that brings the waste products as urine to the bladder.
As the heart beats, pressure within the small blood vessels of the kidney causes blood to be filtered through the glomeruli — a filtrate consisting of water and small substances (such as sugars, amino acids, electrolytes, small proteins, and waste products) is forced into the tubules while blood cells and larger proteins remain in the blood. Then, as the fluid flows down the tubules, the kidneys reclaim the water and substances the body needs and allow the waste products and any excess water to go out into the urine.
In terms of volume, more than 99% of the fluid that is filtered is returned to the blood and less than 1% is excreted.
The kidneys also have some other important functions such as producing a hormone (called erythropoietin) that stimulates red blood cell production by the bone marrow and modifying vitamin D derived from the diet into its final active form (called calcitriol).
Common Symptoms
1. Producing larger volume or urine, drinking more water than before
Dogs typically are taken outside to urinate and, if they are producing more urine and not allowed out frequently enough, they will urinate in the house, which will get the attention of their owners.
The owner also may notice that the dog’s water bowl needs to be refilled more frequently throughout the day. It’s a little more challenging with cats because they normally don’t drink all of the water in the big bowls they typically are provided and they usually urinate in a litter box.
It takes a very observant owner to recognize increased water consumption in a cat, but it’s a little easier to notice when the litter box is filling up with an increasing number of wet clumps of litter and needs to be cleaned out more frequently.
2. Lethargy or weakness
Often misintepretated as normal aging lack of energy. Sleeping more often or less excited when stimulated to play.
3. Loss of appetite or unexplained weight loss
Initial signs may just be picky with food and snacks. Slow muscle loss causing a more evident bony appearence.
4. Vomiting or bad breath with an ammonia/urine-like smell
This may start off as occasional vomit, with cat owner’s may be misinteprated as hair ball issues but eventually the frequency of vomiting increases and coupled with loss of appetite.
5. Poor coat condition or dehydration
Fur coat not smooth and shiny, increase in shedding may occur as well. This symptom can be more generally seen with cats.
6. Elevated Blood Urea NItrogen(BUN) and Creatinine in routine blood chemistry profile
When the concentrations of these particular waste products begin to increase in the blood outside of the normal reference range for the laboratory, the kidneys already have lost about 75% of their function. Later, when the kidneys lose 85% of their function, the concentration of the mineral phosphorus goes up in the blood.
Additional Information On Early Detection
Recently, a new blood test called “symmetric dimethylarginine” or “SDMA” has been introduced that may allow veterinarians to recognize kidney disease much earlier — when the kidneys have lost about 40% of their function. Potentially, the SDMA test could allow us to identify kidney disease in dogs and cats even before the changes in water intake and urine production are recognized.
Common question asked after a pet is diagnosed with CKD is how long their pet will live with chronic kidney disease.
The length of time a dog or cat with chronic kidney disease will live is impossible to predict with certainty because the rate of progression of chronic kidney disease varies considerably among individual animals. Veterinarians can get some idea of the rate of progression of an individual animal’s chronic kidney disease by following the concentration of creatinine in the blood over many months. With the trend of changes in serum creatinine concentration over time being used to estimate how rapidly the kidney disease is progressing. Following progression in this way also can help the veterinarian determine if changes in medical management are helping slow the rate of progression of the disease. Some dogs and cats with chronic kidney disease can live several years with conscientious management of their disease by the veterinarian and pet owner.
If you would like to be more well versed about CKD, an accurate source of information would be from INTERNATIONAL RENAL INTEREST SOCIETY (IRiS).
Below is a simplified pocket guideline from IRiS about the 4 stages of CKD.
