The kidneys are a particularly important part of the body, acting as a filter they also maintain homeostasis and produce a hormone involved in red blood cell production. Sadly, when they go wrong, things can go terribly wrong, so let us take a look at the kidneys in a little more detail, what their function is, and what can go wrong.
Why are the kidneys so important?
These two bean shaped organs have vital functions in the body. They are like the ECU on your car, always sensing what is going on. They monitor fluid levels in the body, control and process waste and play a key role in the release of certain vitamins, minerals and hormones.
But we all know them for their job collecting waste and turning it into urine.
There is a constant supply of blood to the kidneys, it enters through the renal artery and then heads into these structures known as nephrons.
The nephron splits into two nifty mechanisms to filter the blood. This includes the glomerulus and tubule.
The glomerulus acts like a sieve, allowing certain compounds from the blood into the tubule. The tubule then senses whether any of these compounds are needed around the body. If so, they are absorbed. The tubule also senses waste products, like urea which is produced during the break down of protein. It redirects urea as urine which travels down the ureter, into the bladder to be excreted.
You will recognise urea if you have ever come across tests to check kidney function.
Urea is measured through what is known as BUN, or blood urea nitrogen. As we have mentioned, urea comes from the breakdown of protein, and is a completely normal waste product. It is removed by the kidneys, so when kidney function slows down, BUN levels rise. That said, BUN can also rise as protein levels increase.
You will also note creatinine on a lab test, creatinine too is a waste product that comes from muscle activity. Again, it is removed from the blood via the kidneys, but when function slows, creatinine level rises.
Creatinine levels can be used to calculate what is known as glomerular filtration rate, which in short tells you how well the kidneys are filtering and excreting, yet this is seemingly an under-utilised measurement in clinical practice.
Creatinine levels are also used to stage chronic kidney disease.
Stage 1 - <1.4 mg/dl
Stage 2 – 1.4-2mg/dl
Stage 3 – 2.1-5mg/dl
Stage 4 - >5mg/dl
Causes of Kidney Disease
Kidney disease is more commonly associated with the aging pet. Like all things, the kidneys suffer wear and tear carrying out their usual role. As dogs age, function declines.
But there are also cases of acute kidney disease.
Nephrotoxicosis is damage caused by drugs or poisoning – generally when dogs eat something they shouldn’t. In some cases, when diagnosed quickly and treated aggressively, some function can be preserved.
There are however other factors that can play a part in the decline of kidney function.
As we have established, one of the kidney’s main role is to filter helpful and harmful compounds in the blood. It stands to reason that the more harmful compounds it must process, the sooner it reaches its limit.
Frequent chemical exposure is a progression factor in kidney disease and dogs are regularly exposed to cleaning agents, pesticides, and many more environmental toxins. These can be ingested, inhaled, or exposed via the skin.
If you’d like to know more about detoxification of these, then check out our recent blog here.
But the food you choose to feed your dog can also affect kidney function.
Mild dehydration is a risk factor for kidney disease. This is a concern around the moisture content in many commercial foods. Dry-based cereal foods rank low on moisture, with dogs demonstrating increased drinking to counterbalance their water requirement. In cases of mild dehydration, the glomerular filtration rate (that we mentioned earlier) drops, it is this fall in volume that increases the risk of kidney disease.
Dry-based cereal foods also often rank high in starch and being the storage form of energy in plants, starch is converted to sugar when eaten by us or our dogs. Bacteria in the mouth feed off starch and thrive, forming a plaque which can result in periodontal disease. The issue with periodontal disease is when the teeth structures start to degrade. We’ve heard of leaky gut; we can think of it as leaky mouth. Bacteria from the mouth find their way into the blood stream, relocating throughout the body and causing a cascade of other health issues.
When kidney disease develops, there are a range of functions that no longer occur properly:
- Elimination of waste products,
- Production of a hormone involved in the production of red blood cells,
- Maintenance of the body’s fluid balance,
- Metabolism and elimination of certain medications,
- Regulation of electrolytes like potassium and sodium.
Common signs of kidney disease include:
- Appetite loss
- Increased drinking and urination
- Lethargy (tiredness)
- Weight loss
- Unkempt coat (due to decreased grooming)
- Back pain or abdominal pain (may be associated with acute kidney failure)
- Pale gums
But the increase in urination can also be associated with other issues in the urinary tract.
Bladder and Kidney Stones
Struvite stones are a type of bladder stone. Magnesium, ammonia and phosphate are common elements found in the urine and in high enough concentrations they bind together to form crystals that can inflame and irritate the bladder. These crystals can bind together and form stones. They are more common in female dogs and in the older dog. They are often noted in alkaline urine, in cases of high steroid use and where there is abnormal retention of urine. One of the symptoms is increased urination, which can be confused with kidney disease.
Oxalate stones on the other hand are a result of high levels of oxalic acid which is found in foods like wheat and soy. This is another reason why feeding a biologically appropriate diet is key for your dog’s urinary health.
Dogs can also suffer with urinary tract infections (UTI's).
Generally, a UTI occurs when bacteria travel up the urethra and into the bladder. Urine in the bladder is supposed to be sterile, but once bacteria get there, it can reproduce causing a UTI. Some dogs will also develop stones in addition to their UTI. Again, it is more common in female dogs, likely because they toilet closer to the ground. But again, the pH of the urine can either support bacterial growth or impede it; this is why dietary changes are often suggested as part of the treatment.
Less commonly, bacteria can travel through the bloodstream and colonise the urinary tract.
It does however pay to be mindful of UTIs in cases of kidney disease. Reduced kidney function can result in drug concentrations exceeding those normally observed and may cause adverse effects.
How to Support Kidney Health
A biologically appropriate diet is certainly a step in the right direction; having bioavailable nutrients reduces the burden on the body to metabolise them. The moisture content also supports hydration levels. In cases of kidney disease, low phosphorus content is preferable.
Filtered water should always be available for your dog, to aid the elimination of waste products.
If you suspect your dog is experiencing changes with their kidney function, it is essential to seek the advice of your veterinarian. They can help you construct a treatment or management plan.