As young veterinarians, we were taught that “cat’s don’t read the book”. This may seem a strange statement, but absolutely true. Most animal species inherently hide their disease until it reaches a pivotal point. None more so than our feline friends. One of the most common problems that we see is kidney disease and again cats don’t read that book to tell us that there is a big problem under the surface until often times it is critical and life-threatening.
What exactly does the kidney do?
The kidney has several major functions, namely, conserve water, filter out waste products and maintaining electrolyte balance. The kidney is composed of millions of units called nephrons. These little units are the gatekeepers of what stays in and goes out of our body.
So just what happens in the kidney?
- Water conservation: Hydration of the body depends not only on water consumed but on water removed. In times of dehydration, the kidney must respond by conserving water. Similarly, if you drink too much water, the kidney needs to efficiently remove the excess to prevent dilution of the bloodstream. A pet with insufficient kidney function will not be able to make a concentrated urine and will need to drink extra water to process the body’s waste chemicals. For this reason, excessive water consumption is an important early warning sign and should always be investigated. We measure this urine concentration by something called urine specific gravity. The higher the number, the more concentrated it is, the lower the number, the more dilute
- Toxin removal: The kidneys are responsible for removing metabolic waste from the body. If the waste builds up due to a lack of function, we can see certain changes in the bloodwork. SDMA, BUN and Creatinine all increase when the kidneys are unable to perform the job of filtering waste. This is called azotemia, or elevated renal wastes in the blood. Uremia is the name for the clinical signs our pets feel when the azotemia reaches a certain point. Uremia makes a pet feel nauseous, they don’t want to eat, they are very lethargic and often very dehydrated.
- Maintaining electrolyte balance: The kidney plays a major role in controlling electrolyte balance, in particular, calcium and phosphorous regulation as well as conservation of potassium. Unregulated calcium and phosphorous leads to weakening of the bones. Also, insufficient kidneys lose their ability to conserve potassium, this leads to weakness. Supplementation of potassium and phosphate binders, preventing the accumulation of phosphates are often key in treating kidney disease.
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