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The kidneys are two bean-shaped organs found in the lower back. They act like filters, cleaning the blood of the waste products produced by normal metabolic processes (eg, protein breakdown). The kidneys also help maintain body fluids at normal levels.

In most people, kidney function gradually decreases after age 40. Sometimes, the rate of loss of kidney function speeds up in the later years. However, about one third of older adults have no loss of kidney function, suggesting that this is not necessarily an inevitable part of normal aging. In addition, the kidneys have considerably more functional ability than is needed to meet the body's demands. This "reserve" means that older kidneys can continue to clean the blood and maintain normal fluid levels under most circumstances, even with gradual loss of function over time. However, older kidneys are slower to respond to stresses from disease or the environment.

• Signs of Kidney Disease
• Kidney Problems Caused by Disorders of the Blood Vessels
• Problems with the Filtering Structure of the Kidney
• Fluid and Electrolyte Disturbances
  • Problems with sodium regulation
  • Problems with potassium regulation
  • Diagnosis, treatment, and prevention
• Acute Kidney Failure
  • Causes
  • Diagnosis, treatment, and prevention
• Chronic Kidney Failure
  • Dialysis and transplantation

The signs and symptoms seen in kidney problems depend on the underlying disorder. For example, kidney stones may cause sudden, sharp pains in the back or side, while acute (sudden) kidney failure can cause mental confusion, fever, and nausea. Many early kidney problems have no symptoms at first. This is why screening tests to identify problems early are so important.

The first hint of kidney disease may be blood, protein, or pus in a urine sample. These items are tested for in a urinalysis because often they can't be seen with the naked eye. High numbers of red blood cells, white blood cells, or casts can be seen under a microscope. A cast is a clump of protein or white blood cells that takes the shape of the kidney tubules, suggesting that there is inflammation in the kidney. Protein levels in the urine are also measured, and some tests can even distinguish between types of protein (eg, albumin versus antibodies). However, it is important to remember that blood, protein, and pus can reach the urine from sources other than the kidneys (eg, infection of the bladder or prostate).

Signs of decreased kidney function can sometimes be identified on routine blood tests. Increased levels of waste products in the blood that are normally filtered out by the kidneys can be a sign of poor kidney function. Commonly measured waste products include blood urea nitrogen (BUN) and creatinine.

In about half of people over age 60, at least one of the large arteries that supply blood to the kidneys (the renal arteries) is narrowed. Usually, illness does not develop, and this narrowing is never identified. However, sometimes, these blood vessels become blocked, which can lead to severe high blood pressure, progressive kidney disease, or both. Arterial disease of the kidney can also lead to sudden or chronic kidney failure.

Several signs and symptoms suggest blood vessel problems in the kidneys of older adults, including the following:

• the start of severe high blood pressure
• another increase in blood pressure that is already high
• high blood pressure that is not controlled by medications that worked previously
• repeated episodes of lung congestion
• unexplained loss of kidney function

Blood vessel disorders and certain heart problems can cause clots to form in the blood. These clots can travel through the bloodstream and completely plug up or block the renal artery. When this happens, kidney failure may progress slowly, or more obvious symptoms (eg, sudden pain in the side, blood in the urine, high blood pressure, fever, nausea, and vomiting) may be seen. Cholesterol plaques can also break off major arteries and cause a similar problem. There may be changes in blood pressure, changes in mental function, a sudden loss of kidney function, or other signs of a blocked blood vessel in parts of the body.

Several procedures can be used to see if the renal arteries have narrowed. The test that provides the most information is an arteriogram, but it is also the most invasive and risky. In this highly specialized test, a catheter is passed into the large artery in the leg and threaded through the blood vessels toward the heart. A small amount of dye is injected to outline the blood vessels supplying the kidney. An x-ray is then taken of the arteries to see how thick or narrow they are. This test may be needed before surgery. Arteriograms are not usually done if an older adult has diabetes mellitus, chronic kidney disease, uncontrolled high blood pressure, or certain types of cancer because of the increased risk of problems associated with the x-ray dye.

Unless the blood vessel problem is treated, the kidney will continue to have reduced blood flow, leading to higher and higher blood pressure and greater loss of kidney function. The blood vessels can be opened up by several procedures. In an angioplasty procedure, a small balloon attached to a catheter is passed into the narrowed artery and then inflated to open up the narrow area. Other types of surgery can also be done. Both angioplasty and surgery relieve the high blood pressure, but surgery may maintain kidney function better. Treatment of high blood pressure with medications helps, but it does not prevent continuing kidney damage caused by loss of circulation.

The part of the kidney that filters the blood is made up of little ball-like structures called glomeruli (pronounced "glo-mare-you-lie") (Figure: The Kidney, with Common Problem). As blood passes through the glomeruli, waste products are removed and flow outside the body in the urine.

If the glomeruli suddenly become inflamed, this usually causes high blood pressure that begins suddenly, fluid retention (ie, "holding water"), decreasing kidney function, and blood in the urine. This condition has been linked to immune system damage, cancer, and inflammation of the blood vessels.

Another sign of glomerular disease is too much protein in the urine, which is a condition called nephritic (nephrotic) syndrome. About 25% of adults with this syndrome are older than 60 years. Typical signs are fluid retention, a large amount of protein in the urine, and a low amount of protein in the blood. Blood pressure may be high, and some kidney function may be lost.

The most common cause of nephritic syndrome is damage from long-term diabetes. Other causes include amyloidosis (a condition in which a silk-like protein is deposited around blood vessels in the kidney and/or other organs) and multiple myeloma (a cancer that produces excess protein).

Urinalysis, blood tests, and kidney biopsy are used to diagnose glomerular disease. In a kidney biopsy, a small needle is passed through the side of the body to obtain a sample of kidney tissue.

Several types of glomerular disease and nephritic syndrome respond to high doses of corticosteroids, although this treatment can have serious side effects. Blood pressure should be controlled, and the amount of protein in the diet should be limited. Treatment must also address underlying conditions, such as cancer. Unfortunately, glomerular disease often leads to eventual kidney failure.

The kidneys are important regulators of fluid and electrolyte (eg, salt) levels in the blood. They perform this function by excreting hormones (see Hormone Disorders) and by concentrating or diluting the urine. Problems with this regulation system can lead to dehydration or problems with electrolytes. The most serious electrolyte problems usually involve levels of sodium or potassium in the blood.

Older adults are at increased risk of problems with sodium regulation. One common problem is a low concentration of sodium in the blood. This can be from too much fluid or too little salt. Loss of salt is often seen after surgery or after treatment with diuretics (ie, "water pills"). Mild sodium loss may not cause any symptoms, but moderate to severe loss can cause mental and neurologic symptoms, including sleepiness, confusion, seizures, and ultimately coma.

Too much sodium in the blood is often caused by dehydration, which causes fluid levels to go down and salt levels to go up. Dehydration is common in older adults for a variety of reasons (see also Nutrition). Too much sodium initially causes mental symptoms, such as confusion, listlessness, and coma, brought on by loss of water and shrinkage of brain cells. Changes in blood pressure, pulse rate, and skin flexibility develop as dehydration worsens.

The list of potential causes for loss of potassium in older adults is long. Low potassium may be secondary to gastrointestinal losses, as happens with vomiting, diarrhea, and using too many purgatives and enemas. Potassium may also be lost through the kidneys, which is a common problem when someone is taking diuretics (ie, "water pills"). Potassium can also be lost from an underlying kidney disease and in some hormone disorders.

When the body does not have enough potassium, the heart and vessels, the nervous system, muscles, and kidneys are all affected. Common signs and symptoms include irregular heart rhythms, weakness, tiring easily, cramping, muscle tenderness, and urinating a lot.

Too much potassium in the blood is seen in people with chronic kidney disease. However, this rarely becomes a serious problem until another problem adds to it. Possible additional problems include too many potassium supplements, certain drugs, and hormone deficiencies. Drugs such as nonsteroidal anti-inflammatory drugs (NSAIDs), angiotensin-converting enzyme (ACE) inhibitors, and diuretics (ie, "water pills") are especially common causes of too much potassium developing suddenly in older adults.

Urine and blood tests are used to identify fluid and electrolyte disturbances. Treatment involves correcting the imbalance with appropriate fluids and/or supplements. The underlying problem is usually corrected gradually to avoid causing a problem in the other direction.

Prevention is best. Electrolyte levels should be monitored regularly, especially during hospitalization, hot weather, diuretic use, or salt restriction. On very hot days, it is sometimes necessary to decrease the dosage of diuretics as well. Proper nutrition is very important, especially for people taking diuretic drugs. For example, bananas are a good source of potassium and are often recommended for people taking certain types of diuretics.

Older adults should drink enough fluid throughout the day, especially during hot weather or when there is no air conditioning. In fact, you should try to drink plenty of fluids even if you don't feel thirsty, because the thirst response is blunted as we age. This thirst response is decreased even more in people with brain diseases, such as stroke or Alzheimer's disease. It is important to remember that mental or physical disability can significantly cut down on fluid intake. For example, a disabled person may find it difficult to get up to take a drink of water. A supply of fresh water should always be kept close at hand.

Older adults are at increased risk of kidney failure because of age-related changes that occur in the kidney. Kidney failure is especially common in hospitalized older adults. Acute or sudden kidney failure can be caused by disease within the kidney, severe dehydration, problems in regulating blood flow through the kidney, or urinary tract blockage. These problems can lead to either sudden or gradually progressive kidney failure. A person with sudden kidney failure often feels feverish and weak. The build up of toxins (ie, poisons) can also cause behavioral or mental changes (eg, confusion or delirium), which are usually reversible.

Many conditions reduce blood flow to the kidneys, which in turn decreases the ability of the kidneys to produce urine. Dehydration is one of the most common causes in older adults because of age-related changes in kidney function that increase the risk of losing salt and water. Diuretics (ie, "water pills") can make the problem worse. Low blood pressure, heart failure, blood vessel disease involving the kidney, and other conditions or medical procedures can make the situation worse. For example, because people in the hospital are usually not allowed to eat or drink before many medical and surgical procedures, they can tend to get dehydrated.

Many medications can injure the kidney and cause kidney failure. Occasionally, an allergic reaction to a medication (such as the dyes used in x-ray studies) can injure the kidney. Certain antibiotics, x-ray dyes, and NSAIDs can also cause damage and sudden loss of kidney function. Damage from drugs can be even greater when there are underlying conditions, such as heart failure, diabetes, liver failure, or dehydration. NSAIDs (eg, ibuprofen, naproxen) are an especially common cause of kidney damage, because these over-the-counter drugs are used commonly for pain relief.

Loss of kidney function is often linked to problems within the kidney tubules, which help adjust the concentration of acids and salts in the urine. Problems with the kidney tubules can be caused by poor blood flow or specific kidney toxins (poisons). Many antibiotics needed to treat serious infections have been linked to problems with kidney tubules. Low blood pressure during and after surgery, fluid loss after surgery, and heart rhythm problems may also contribute to poor blood flow.

Acute or sudden kidney failure can also be caused by extreme damage to the muscles of older adults. Muscle damage may develop in a person who cannot move around because of illness, or who has fallen and been unable to get up for a long time. When muscles die, they can release substances into the blood that are toxic to the kidney.

Blockage of urine flow is also a frequent cause of kidney failure in older adults. The flow of urine can become blocked for a variety of reasons, including changes in body structures, damage to valves within the urinary system, kidney stones, or tumors. In men, the most common cause is a prostate that is enlarged or cancerous. In women, likely causes include a change in the position of the uterus, or cancer of the uterus or ovaries. Nerve disorders can affect the ability of the bladder to contract, which can cause blockage, especially in people with diabetes. In addition, medications can cause a blockage by interfering with nerve reflexes.

Urinalysis, blood tests, imaging studies (eg, x-rays), and kidney biopsies are commonly used to diagnose acute or sudden kidney failure. An ultrasound of the kidney is especially useful to look for blockage or other problems within the kidney. Ultrasound uses sound waves to produce pictures of the underlying tissues, avoiding the use of x-ray dyes.

Treatment for sudden kidney failure depends on the underlying cause.

Careful monitoring and watching for complications (eg, heart failure or infection) are important in managing kidney failure. In severe cases, dialysis may be needed to remove poisons or toxins from the blood while the kidney recovers function. Dialysis is a technique that uses the abdominal cavity or a machine to filter and clean the blood.

Prevention involves avoiding situations that can lead to sudden kidney failure, especially in people undergoing medical tests or procedures in the hospital. This includes carefully evaluating the need for medications or an x-ray dye test, maintaining good hydration, and carefully monitoring kidney function. Daily changes in fluid intake, urine production, weight, and blood pressure are usually measured. If a medical procedure is delayed, ask about "nothing by mouth" instructions so that you don't go for extended periods without adequate fluid intake.

In chronic kidney failure, kidney damage has gradually progressed over a long time from poorly controlled high blood pressure or diabetes, blood vessel problems, or other kidney disorders (eg, glomerular disease). Waste products build up in the blood, which causes nausea, vomiting, and mental problems. Chronic kidney failure is also linked to hormone problems that can lead to anemia and osteoporosis. Chronic kidney failure ultimately leads to end-stage kidney disease and complete loss of kidney function, although this progression can take 10-20 years. People with end-stage kidney disease need either regular dialysis to clean the blood or a kidney transplant.

When chronic kidney disease is suspected, you may be referred to a nephrologist, who is an expert in kidney diseases, for the following:

• determine the type and severity of kidney disease
• develop a treatment plan that maximizes kidney function while both controlling underlying problems (eg, diabetes and high blood pressure) and minimizing potential complications (eg, heart disease or nutritional deficiencies)

Older adults with end-stage renal disease are usually placed on dialysis. Diabetes, high blood pressure, glomerular disease, and kidney blockage are the most common causes of end-stage renal disease in older adults.

There are two commonly used forms of dialysis. In hemodialysis, you sit in a chair for several hours one or more times per week, while your blood is siphoned into a machine that filters the waste products and then returns the clean blood to you. In peritoneal dialysis, solutions are pumped into your abdomen to draw out the waste products from the blood. The excess solution and waste products are then removed from the abdomen. The choice of hemodialysis or peritoneal dialysis depends on your wishes and overall condition, as well as available resources. Survival rates for both procedures are about the same.

Another possibility for management of end-stage renal disease in older adults is a kidney transplant. Results of this procedure have improved dramatically over time. However, kidney transplants remain uncommon in older adults. Some older adults have underlying medical conditions that would interfere with successful transplantation. Of course, the biggest problem is that there are not enough kidneys donated and available for transplantation.