Chronic Kidney Disease and Failure (CKD, CRF, CRD)
Chronic kidney disease is defined as kidney disease that has been present for months to years.
Chronic renal disease (CRD), chronic renal failure (CRF), and chronic renal insufficiency refer to the same condition.
CKD is not a single disease. There are many different causes of CKD but by the time the animal shows signs of kidney disease the cause may no longer be apparent.
Some potential causes of CRF include:
- congenital malformation of the kidneys (birth defects)
- chronic bacterial infection of the kidneys with or without kidney stones (pyelonephritis)
- high blood pressure (hypertension)
- diseases associated with the immune system (e.g. glomerulonephritis, systemic lupus)
- acute kidney disease, for example poisoning with antifreeze, that damages the kidneys can lead to CKD
Structure of the kidneys
The microscopic unit of the kidney is called the nephron. Each kidney contains thousands of nephrons. When the pet is young and healthy not all nephrons are working all of the time; some nephrons are held in reserve. As the animal ages or if the kidneys are damaged, some nephron s die and other resting nephrons take over the work of those that die. Eventually all the remaining nephrons are working. When there are no extra nephrons remaining and kidney damage continues the pet will start showing signs of CKD. Because of this stepwise loss of nephrons the kidneys are able to “hide” the fact that they are damaged until the damage is severe. When 2/3 of the nephrons have been lost the pet is no longer able to conserve water and the pet passes larger amounts of dilute urine. By the time a pet has an elevation in thewaste product creatinine in its blood, 75% of the nephrons in both kidneys have been lost.
What do the kidneys do?
What do the kidneys do?
When blood flows through the kidneys, the kidneys act as a complex filter that removes from
blood wastes that are generated from break down of food, old cells, toxins or poisons and many
drugs that are given for treatment of other diseases. The wastes are removed with water as urine. Waste products than can be measured in the blood include creatinine and urea nitrogen but there are many other waste products that are not measured by blood tests. The kidneys also acts as a filter to keep “good” substances in the blood. The kidneys regulate the amount of water in the blood by excreting extra water and retaining water to prevent dehydration by varying the amount of urine that is produced. The kidneys help regulate blood pressure by saving or eliminating sodium based on how much sodium the pet is eating. The kidneys helpregulate calcium and vitamin D which keep bones strong. The kidneys produce a substance that helps with the creation of new red blood cells. Because the kidneys have so many functions, when the kidneys are not working normally, there are many signs that the pet may show. CKD is progressive.
By the time the pet shows signs of CKD, the damage is severe. There is no cure for CKD. The remaining nephrons are working so hard that with time they will fail as well. CKD is usually fatal in months to years but various treatments can keep the pet comfortable and with a good quality of life for months to years.
Signs of CKD
Because the kidneys perform so many functions, the signs pets with CKD show can vary quite a bit. The signs may be severe or may be subtle and slowly progressive. Despite the chronic nature of the disease, sometimes signs appear suddenly.
Some of the more common signs of CKD include:
- drinking too much (polydipsia) and urinating large volumes of urine (polyuria)
- the increased volume of urine in the bladder may lead to, or worsen incontinence (leaking urine), especially at night
- vomiting and/or diarrhea
- lack of appetite and weight loss
- general depression related to the elevation of waste products in the blood
- anemia resulting in pale gums and weakness due to a low blood count
- overall weakness from low blood potassium
Less common signs include:
- weakened bones can result in bone fractures
- high blood pressure can lead to sudden blindness
- itchy skin from calcium and phosphorous depositing in the skin
- bleeding into the stomach or gut or bruising of skin
Signs you may see if you examine your pet include: dehydration, weight loss, pale gums and ulcers in the mouth.
The signs seen in pets with CKD and the findings on examination are not specific for CKD and may be seen with many other diseases so blood and urine tests are needed to make a diagnosis of CKD.
Abnormalities that are often seen on diagnostic blood and urine tests include:
- anemia without signs of a response by the body to the low blood count (non regenerative anemia)
- increased wastes that are normally removed by the kidneys (blood urea nitrogen [BUN] and creatinine)
- increased phosphorus
- Calcium is often normal but can be elevated in some pets with CKD and rarely is decreased
- dilute urine
- +/- protein or bacteria in the urine
Sometimes bruising occurs where the blood sample was drawn as pets with CKD may have platelets that are less sticky than normal (normal platelets prevent bruising).
A diagnosis of CKD can usually be made based on the signs, physical examination and blood and urine tests but other tests may be performed to look for an underlying cause for the CKD and/or to “stage” the CKD.
Other tests that may be performed include:
Determination of kidney size using abdominal radiographs (x-rays) or ultrasound
The kidneys in pets with CRD are usually small reflecting the death of a large number of nephrons. If the kidneys are large then certain causes for the CKD should be considered such as lymphoma (cancer) of the kidneys, or an uncommon disease called amyloidosis. Some pets with signs of kidney disease who have large or normal sized kidneys may have acute kidney failure rather than CKD. The treatment and prognosis for pets with acute kidney disease differs from the treatment and prognosis of pets with CKD.
Kidney biopsy
A biopsy is not required to make a diagnosis of CKD but the results of a biopsy may show a cause for the CKD. A biopsy is more likely to show specific information when the kidneys are big rather than small. A biopsy can be valuable in pets who develop CKD at a young age or who are of a breed known to develop congenital kidney disease. There may be specific microscopic changes in a kidney biopsy from an animal with congenital kidney disease that may suggest that related animals are also at risk for developing CKD. Knowledge that the cause of CKD is caused by congenital kidney disease does not change the treatment of the affected animal but does provide information for related animals, for example if you should remove them from a breeding program. When a biopsy is planned, usually the biopsy is collected using ultrasound or laparoscopy to see the kidney during the biopsy so that no other organs are damaged during the biopsy.
Tests of clotting ability
If a pet is going to under go kidney biopsy, tests may beperformed in advance to evaluate the ability to stop the bleeding from the biopsy site.
Treatment of CRF
The severity of the pet’s signs will determine what treatments are needed. Not all treatments presented below may be needed or appropriate for each pet with a diagnosis of CKD. Treatments may also be started incrementally (a few treatments are started and then based on patient response, additional treatments may be added later).
Pets with severe signs may be hospitalized for fluid and intravenous drug treatment to reduce the amount of waste products in their body. Many pets with CKD will feel better in response to treatment with IV fluids but if the kidney disease is extremely severe the pet may not respond to treatment.
Those pets who are still eating and not showing severe signs are treated with a variety of treatments, often introducing treatments incrementally as new signs develop. The treatment approach is often called “conservative”. Remember that CKD is not adisease that can be cured. Treatments are designed to reduce the work the kidneys need toperform, to replace substances that may be too low (such as potassium) and to reduce wastes that accumulate such as urea (generated by the body from proteins) and phosphorus. The initial response to conservative therapy may be relatively slow, taking weeks to months to see a response.
Bacterial culture
Bacterial infection is not a common cause of CRD but pets with CKD may develop a bacterial infection as several aspects of the pet’s immune system may be less functional when the kidneys are failing. If white blood cells are observed on microscopic examination of the pet’s urine, a bacterial culture of the urine should be obtained.
Diet
Feeding of a kidney diet is usually recommended. Kidney diets contain less protein compared to other commercial diets and the protein is high in quality. It is protein in the diet that is converted to wasteproducts that the kidneys must remove in the urine. The higher the quality of the protein in the diet, the less wastes created for the kidneys to eliminate. Low quality protein requires the kidneys remove more wastes. which makes them work harder. Egg and meat contain higher quality protein; cereal grain protein is of lower quality which leads to more wastes for thekidneys to eliminate. Protein is used by the body to repair cells and tissues that are continually regenerating, so a pet needs some protein in their diet. By feeding a low quantity, but high quality protein diet that contains an appropriate amount of fats and carbohydrates, the pet’s body can use the protein for replacing the cells and tissues and use the fat and carbohydrates for energy. Kidney diets also contain a lower amount of phosphorus. Phosphorus accumulates in the blood when the kidneys are diseased. Kidney diets control the amount of other substances that may be too high or too low in patients with CKD such as salt, potassium, magnesium and B vitamins. There are differences in the kidney diets for dogs and cats. When making diet changes it is often beneficial to gradually introduce the new diet by adding increasing amounts of the new diet while reducing the amount of the current diet over 1 to 2 weeks. The pet is more likely to accept a new diet when it is introduced gradually and it is less stressful to the kidneys to gradually adapt to changes in the diet.
Protein restricted diets are less palatable than higher protein diets. Pets with CKD that are still eating are more likely to accept a change in diet to a protein restricted diet than are pets who are very ill and refusing most foods. Protein restricted diets are more expensive than higher protein diets.