What Does the Kidney Do?

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Normal Kidney Function

A person normally has two kidneys located at either side of the spine behind the abdominal organs and below the rib cage. They are bean shaped and weigh about one-third of a pound. When working properly, your kidneys perform five main functions:

  1. Clean waste material from the blood
  2. Retain or excrete salt and water
  3. Regulate blood pressure
  4. Stimulate bone marrow to make red blood cells
  5. Control the amount of calcium and phosphorous absorbed and excreted

    How Your Kidneys Work

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Types and Causes of Kidney Disease

Many things can lead to loss of kidney function. Although there is not enough space to list all possible causes here, a general list includes:

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Signs and Symptoms of Kidney Disease

The signs and symptoms of kidney disease are varied and depend on the type of problem and the extent of kidney impairment. Frequently however, patients may not experience any symptoms until kidney disease is advanced. Early signs that the kidneys may be diseased include blood or protein in the urine or elevated blood pressure readings. Blood and urine testing more accurately define the degree and nature of the problem. The National Kidney Foundation is running a screening program for the early detection of kidney disease. The KEEP (Kidney Early Evaluation Program) initiative is ongoing throughout the United States. Here in Maine, the NKF has run many such programs which have identified many individuals at risk for the development of hypertension and kidney failure (NKFM-KEEP). There are, however, some common symptoms of kidney disease. They appear as one or more of the five basic functions of the kidney begin to fail:

Should an individual have any of these problems, a detailed evaluation should be performed in order to make a diagnosis thus guiding therapy and also defining the likely outcome. In general, the earlier kidney conditions are diagnosed and treated, the better the outcome is likely to be.

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Treatment of Kidney Disease

The earlier that kidney disease is detected, the sooner treatment can be started that can slow down or stop the loss of kidney function. For example, various forms of nephritis can be treated by suppressing the immune reaction that leads to kidney damage. Another example is the use of specific types of blood pressure medications (ACE inhibitors and ARIIB receptor blockers) which have been proven to inhibit progressive kidney damage in diabetes as well as other diseases. The following table describes the "stages" of chronic kidney disease, and the focus of treatment at each level.

StageDescriptionPercent Kidney


Kidney damage with normal or increased glomerular filtration rate> 90Screening, chronic kidney disease risk reduction


Kidney damage with mild decrease in glomerular filtration rate60-89Diagnosis and treatment, treatment of comorbid conditions, slow progression of kidney failure, cardiovascular disease risk reduction


Moderate decrease in glomerular filtration rate30-59Estimating progression of renal disease


Severe decrease in glomerular filtration rate15-29Preparation for renal replacement therapy


Kidney failure< 15 (or dialysis)Replacement therapy (dialysis or transplantation)

High Blood Pressure: How is it Treated?
Sodium and the Kidney
Low Protein Diet
Staying Fit with Kidney Disease
Weight Loss and Control

Treating end stage renal disease: Although specific symptoms of kidney disease can be treated with various types of therapy, including diuretics, blood pressure medications, and erythroipoietin therapy, once the kidneys lose more than 85-90% of their ability to function, some type of renal replacement therapy must be considered. That is, something must be done to replace the function of the kidneys. The two main types of replacement therapy are dialysis and kidney transplantation. These are discussed more detail below.

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Dialysis partially replaces two of the functions lost with kidney failure. It removes many of the toxic waste products that build up in the blood and body tissues, and removes the excess salt and water that accumulates when urine production is low. Dialysis can assist in controlling blood pressure by removing excess fluid, but in some cases high blood pressure medications are still necessary.

Dialysis cannot affect the anemia or bone problems caused by kidney failure. These problems are treated with specific medications. Dialysis will not harm the kidneys, but cannot make failed kidneys function again.

There are two principal types of dialysis and each has its advantages and disadvantages. They are:

  1. Hemodialysis: Hemodialysis is performed by inserting a needle into some type of "access" which has been surgically created, and pumping the blood through a dialysis machine. Toxins are removed and needed chemicals are added, and the blood is returned to the patient via a second needle. Hemodialysis can be performed either in an outpatient dialysis center or at home with the aid of a trained family member.


  2. Peritoneal Dialysis: In peritoneal dialysis dialysis, dialysate fluid is instilled into the abdomen through a small flexible tube which has been surgically placed. The fluid is allowed to dwell in the abdominal cavity for a period of hours, then drained and replaced with fresh fluid. This can be done either during the day or overnight while the patient is sleeping.

    Peritoneal Dialysis

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Kidney Transplantation

Another form of renal replacement therapy is kidney transplantation. In this form of therapy, a kidney is taken from one person and surgically implanted in a person with irreversable kidney failure. Not everyone is a candidate for transplantation, and it is not a "cure" for your kidney disease. There are two types of kidney transplants:

  1. Living Donor Transplantation: In this type of transplant, the kidney comes from a living donor. It may be a blood relative ("living related") or a spouse, friend or other individual ("living unrelated").
  2. Deceased Donor Transplantation: In this type of transplantation, the kidney comes from a person who has died, and is the result of the generosity of the donor's family.

For more information on kidney transplantation and organ donation, check out our Transplantation page or Links of Interest page for links to several transplantation and organ donation sites.

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