What is residual kidney function?
Kidneys are fist-sized, bean-shaped structures located in the middle of your back on both sides of your spine. Each kidney contains about one million tiny filtering units called glomeruli.
Your kidneys are your body’s internal filtration system. They continually remove waste and extra fluid from your blood to keep you healthy. The kidneys filter about 200 quarts of blood daily and remove about two quarts of waste products, toxins and extra water in the form of urine.
The kidneys also regulate blood pressure and help keep your heart healthy. Kidneys release hormones and other chemicals into the blood stream, help with red blood cell production and maintain the right amount of potassium, phosphorus and calcium in your body.
What happens when your kidneys fail?
Kidney failure refers to reduced function of the kidneys. As the kidneys’ ability to function decrease, glomeruli lose their ability to filter. This causes waste products to remain in the blood and often reduces the body’s ability to get rid of extra fluid. Without working kidneys, fluid and waste products accumulate in the body causing swelling (edema) and symptoms such as nausea, decreased energy due to anemia, decreased appetite, shortness of breath and itching.
Chronic kidney disease (CKD) progresses through five stages. In the first three stages, there are increasing levels of kidney damage often without any noticeable symptoms. In the early stages of kidney failure, there may be no symptoms, but it is common for these people to have high blood pressure, swelling of the legs and/or congestive heart failure. In stage four, waste products collect in the blood and usually begin to cause symptoms. In stage five, also known as end stage renal disease (ESRD), about 1/10 of normal kidney function remains, and the kidneys cannot regulate the body’s balance of salt and water. Production of urine slows or stops altogether.
Kidney disease is detected through urine tests for blood or protein, X-rays or scans of the kidneys and/or blood tests to measure kidney function. The presence of protein in the urine is generally an indicator of kidney damage.
What is residual kidney function?
When referring to your kidneys, residual kidney function — or residual renal function — is the term used to describe how much of your kidney function remains once your kidneys have started to fail. Once your kidneys begin to fail, your residual renal function is a measure of how much function is left. People on dialysis with residual kidney function will continue to make urine, although the amount of toxins being excreted in the urine will vary and need to be measured. When residual kidney function is gone, no urine is made.
Even after you start dialysis, it is critical to try to preserve residual kidney function for as long as possible because it improves your overall health and well-being and allows you to drink more liquids. Studies have shown that preserving residual kidney function for as long as possible leads to better survival rates in people on dialysis. Residual renal function helps maintain the body’s fluid and potassium levels and assists with the removal of wastes. When a dialysis patient’s residual renal function declines, more waste products, potassium, phosphorus and fluid build up in the body. When this happens, the dialysis prescription needs to be changed so that blood can be cleaned for a longer time. If blood isn’t cleaned enough, the level of toxins in the body will rise, which can affect appetite resulting in malnutrition.
How can I preserve my residual kidney function?
If lab tests show that you are in the early stages of kidney failure, your doctor will work with you to keep your kidneys functioning for as long as possible. One thing your doctor may do first is put you on blood pressure medicine. Certain blood pressure medicines cause your blood vessels to widen so that more blood can flow through them. This puts less stress on the kidneys’ filtering units or glomeruli. If you are diagnosed with chronic kidney disease (CKD), your target blood pressure should generally be 130/80 or less.
Your doctor may also refer you to a renal dietitian who can help you plan a diet that meets your nutritional needs while limiting the work your kidneys have to do to process your food. This diet will likely limit foods high in potassium, phosphorus, sodium and protein. However, since each person is different, your renal dietitian will work with you to come up with a diet that is tailored to your specific needs. Many people have been able to keep their kidneys functioning for years simply by following the diet their dietitian designed for them, taking their prescribed medications and keeping blood pressure and diabetes under control.
Exercising regularly, maintaining a healthy weight and not smoking are also important factors in preserving kidney function.
Can I still preserve residual kidney function when I start dialysis?
If your kidney function drops to 10 or 15 percent of normal, dialysis will be needed to clean your blood. Dialysis takes the place of healthy kidneys and helps keep your body in balance by:
- Removing waste, salt and extra water to prevent them from building up in the body.
- Keeping a safe level of certain salts in your blood, such as potassium, sodium and bicarbonate.
- Helping to control blood pressure.
One way to preserve residual kidney function once dialysis is needed is to choose peritoneal dialysis (PD) as your first method of dialysis. Peritoneal dialysis appears to help protect residual renal function better then hemodialysis.
Peritoneal dialysis has been shown to preserve residual kidney function because it is gentler on the body. PD is gentler because it is done daily so there are fewer shifts in fluid volume than with in-center hemodialysis. Many PD patients keep enough residual kidney function to create urine for awhile. PD also makes it possible for patients to increase the length and frequency of their dialysis treatments as their residual kidney function declines. This is called incremental therapy. This kind of gradual build up of treatment is generally not possible with in-center hemodialysis, where 90 percent of patients start out doing treatments three times a week for three to four hours per treatment. Sometimes patients start out on PD treatments and then switch to hemodialysis later on.
Summary
Residual kidney function is the amount of kidney function you have left once your kidneys have started to fail. Although chronic kidney failure is irreversible, medicines and diet may help slow its progression. In some cases, kidneys can continue to work for years without leading to kidney failure. Kidney disease sometimes happens so gradually that symptoms do not appear until end stage renal disease. If kidney disease progresses to end stage renal disease and dialysis is needed, starting out on peritoneal dialysis (PD) may help preserve residual kidney function because it is gentler on the body than in-center hemodialysis.
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