Dogs and cats can suffer from either acute or chronic renal failure caused by many different types of illnesses.
Did you know...
In humans, you can donate one kidney to a close relative and live a happy normal life. Should your remaining kidney lose up to 50% of its ability to concentrate urine, you can still appear normal although you may be drinking a bit more and making dilute urine. Kidney blood tests can be normal even at this stage.
In other words, you can loose 3/4 of your total kidney function
and still have normal kidney blood tests
What happens in kidney (renal) failure?
The same "1/4 functioning rule" applies to dogs and cats. A Senior Pet Health Check urine examination looks at the concentrating ability of the kidneys to detect early reduction in kidney function. The earlier it is detected, the easier it is to treat.
Trying to keep the remaining healthy 1/4 of kidney functioning is the name of the game in veterinary medicine. Vets are normally unable to offer dialysis and/or kidney transplants for their older patients. Dialysis is performed in people with renal failure to filter out the waste products that the kidney normally places in the urine. When a donor kidney becomes available, they don't need the dialysis any more.
Kidneys place waste products from normal day to day bodily functions in the urine e.g. waste products from protein rich meals (urea and creatinine), phosphate. When we run blood tests on renal failure cases, we see elevated levels of urea (Blood Urea Nitrogen- BUN), Creatinine and Phosphate. As mentioned before, elevation of these test results means we are already dealing with less than 1/4 of remaining healthy kidney function.
Kidneys also re-absorb a lot of water that would otherwise escape into the urine. In other words, they make the urine concentrated.
If the kidneys are failing, they are unable to concentrate urine. In other words, the pet makes more urine than normal because the kidneys can't re-absorb the water out of the urine like they did when healthy. More urine going out of the body automatically triggers a chemical release in the brain which makes the pet thirsty. So we see increased thirst and increased volume of urine in renal failure.
Kidneys have powerful protective mechanisms in place which kick into action if problems arise. One of these is a link to the brain to control blood pressure. If the kidneys are not working properly, chemicals are released which elevate the blood pressure in an attempt to improve the flow of blood through the kidney and remove waste products that are building up in the body.
Kidneys are also responsible for sending messages to the bone marrow telling it to make more red blood cells (RBC's) to replace the old ones which are "gobbled up" by the spleen and liver when they are worn out. If there is only 1/4 of normal kidney left, these messages to the bone marrow decrease and quite often, a pet in renal failure is anemic (low numbers of red blood cells). Because RBC's are responsible for carrying oxygen around the whole body, the pet is quite weak and easily fatigued.
Causes of acute renal failure
- Addison's disease
- Cancer e.g. Lyphosarcoma
- Inappropriate use of drugs such as NSAID's and ACE inhibitors
- Inability to urinate e.g. stones (uroliths, FUS/FLUTD), prostate disease
- Poisons: grapes, sultanas, marc -see Grape and Sultana Toxicity
- Reduced blood pressure e.g. anaesthesia
Causes of chronic renal failure
- Normal wear and tear in old age
- Genetic e.g. polycystic kidney disease in Cairn Terriers, cats
What are the signs of renal failure?
- Bad breath (halitosis)
- Excess thirst and increased volume urine
- Poor appetite
- Weight loss
How do you diagnose kidney failure?
As with most diseases, early detection and treatment is much more preferable especially for a vitally important organ like the kidneys. We would rather diagnose renal failure before clinical signs or blood tests indicate its presence. In other words, before the pet is down to its last 1/4 of healthy kidney tissue.
Urine Protein:Creatinine Ratio
We like to run a urine test called a Protein:Creatinine ratio which can detect kidney failure long before a pet is down to it's last 1/4 of healthy tissue. It is very accurate at detecting early kidney problems long before blood tests start to indicate a problem.
For all our renal failure cases, we use a Doppler machine to record elevations in blood pressure and measure response to blood pressure lowering medications.
What treatments are available?
Failing kidneys are not filtering waste products from meals into the urine. They build up in the body and make pet feel off colour and nauseous. That is why they sometimes vomit son after a protein rich meal. We can minimise this buildup by feeding special diets e.g. Hill's Kidney Diet (K/D) which are low in protein and high in carbohydrates and fats.
Other standard treatment for renal failure cases include:
- Appetite stimulants for cats who are picky eaters e.g. Pericatin (an anti-histamine)
- Force feeding using a stomach tube through which fluids and liquidised renal support diets can be administered.
- For cases with elevated Phosphorous in their body, we can use drugs called phosphate binders.
- IV Fluids for very ill pets: a) Intravenous for short term management in hospital to try and flush the waste products out through the kidneys and correct dehydration.
b) Sub-cutaneous fluid therapy at home using a long-term sub-cutaneous catheter under the skin.
How can success of treatment be monitored?
We like to repeat the urine Protein:Creatinine ratios and/or blood tests on a regular basis to measure response to therapy.
All in all, renal failure cases can be very difficult to treat, mainly because most cases are down to their last 1/4 of healthy kidneys.
For young cats in Australia with kidney failure, there is the possibility of kidney transplantation in Brisbane, but it is quite involved and the donor cat has to be taken on as a new family pet. It means life long treatment with anti-rejection drugs e.g. Cyclosporine which can mean the whole exercise is very expensive.