Kidney disease is a general term for any damage that reduces the functioning of the kidney. Kidney disease is also called renal disease.
The kidneys are a pair bean-shaped, fist-sized organs that are located below the rib cage near the middle of the back. In adults they filter about 200 quarts (190 L) of blood every day to remove waste products that result from the normal activities of tissues in the body. These wastes circulate in the blood. and if not removed they would damage the body. The kidneys also play a crucial role in regulating the amount of water and chemicals (electrolytes) in the body such as sodium, potassium and phosphorous.
Inside the kidneys are about one million tiny units called nephrons. Inside each nephron is a very thin blood vessel called a capillary that twists around a very thin tube called a tubule. This combination of capillary and tubule inside the nephron is called a glomerulous and it is here that the blood is filtered. Water, electrolytes, and waste products (but not red blood cells) can pass across the capillary wall and into the tubule. The kidney then regulates how much water and which other substances can pass back into the blood in the capillary to keep the body in balance. Waste products, excess water, and excess electrolytes remain in the tubule and eventually leave the body as urine.
The kidneys also release three regulatory chemicals—erythropoietin, renin, and calcitriol—that affect other functions in the body. Erythropoietin stimulates the bone marrow to produce new red blood cells. Renin helps regulate blood pressure, and calcitriol is a form of vitamin D and is important in maintaining bones and the level of calcium in the body.
Because the kidney has many functions, there are many types of kidney disease. Congenital kidney diseases are disorders that are present at birth. Polycystic kidney disease (PKD) is a rare disorder in which children inherit defective genes from both parents that cause cysts full of fluid to develop in the kidneys and replace the blood filtering units. As a result, the kidneys cannot adequately remove wastes from the body. There are two other types of PDK. One is inherited, but does not appear until adulthood, and the other develops as a result of long-term kidney damage. In total, about half a million people in the United States have some form of PKD. Hereditary disease and birth defects are the most common causes of kidney disease in children up to age 14.
Acute kidney diseases are problems that develop suddenly. Many acute kidney diseases can be cured, but some may cause permanent damage. Common acute kidney diseases include kidney infection, hemolytic uremic syndrome, nephrotic syndrome in children, and damage caused by injury to the kidney or poisoning. Hemolytic uremic syndrome is a rare disease that usually affects children under age ten and is caused by eating food contaminated with bacteria. The bacteria release a poison that damages the kidney and causes acute kidney failure. Most children who develop this disease recover and their kidney function returns to normal.
Chronic kidney disease is disease that is slow to develop and usually does not show any symptoms until kidney damage is permanent. The National Kidney and Urologic Disease Information Clearinghouse, a federal agency, estimates that about 4.5% of people over age 20 have chronic kidney disease as indicated by tests that measure kidney function. The most common cause of chronic kidney disease in the United States is diabetes. It accounts for between 33% and 40% of all new cases of chronic kidney disease in the United States. In diabetes, the body cannot break down glucose (sugar). This extra glucose in the blood damages the nephrons so that they no longer filter blood effectively.
High or uncontrolled blood pressure (hypertension ) is the second leading cause of chronic kidney disease. It accounts for between 27% and 30% of all new cases of chronic kidney disease. High blood pressure damages the capillaries in the nephron, so that they can no longer work with the tubules to filter the blood. Glomerulonephtitis is a term for several different chronic kidney diseases where damage to the nephrons causes protein or red blood cells pass into the urine. Kidney cancer is uncommon, accounting for only 2% of cancer cases.
Over-the-counter analgesics (pain medications) such as aspirin, acetaminophen (Tylenol), ibuprofen (Advil), naxopren sodium (Aleve), and similar medications that can be bought without a prescription may make kidney disease worse in individuals who already have kidney damage or cause kidney damage in healthy individuals who take these medications daily for several years. The chance of damage is increased when these pain medications are taken in combination with each other or with caffeine or codeine (Some painkilling tablets are a combination of pain medications and caffeine or codeine). Individuals who take these painkillers regularly or who have been told they have kidney damage should discuss the risk of these medications with their physician.
Chronic kidney disease can lead to end-stage renal disease (ESRD), in which there is almost total failure of the kidneys. If renal function is reduced to only 25% of normal, serious illness results. When this drops to 10-15% of normal, death occurs unless the individual receives dialysis or a kidney transplant. In 2002, there were over 100,300 new cases of ESRD, 44% of which were caused by diabetes. Treatment of ESRD in the United States cost about $25.2 billion in 2002.
Causes & symptoms
Causes of kidney disease are many and varied. Leading causes are diabetes, high blood pressure, inherited disease, and infection. Acute kidney disease is often marked by a lack of urination and increased fluid build up in the body. Chronic kidney disease is often called a "silent" killer, because no obvious symptoms develop until the kidneys are permanently damaged. The National Kidney Foundation estimated in 2005 that 20 million Americans had undetected moderate chronic kidney disease. Chronic kidney disease most often results from other diseases such as diabetes or hypertension.
Simple blood and urine tests can indicated kidney disease, but more extensive testing may be needed to determine the exact nature of the disease. A blood test that measures serum creatinine, a waste product, can indicate how well the kidneys are working. Although normal levels of creatinine vary (an average range is 0.6-1.2 mg/dL), a higher than expected level in the blood may indicate kidney damage. A blood urea nitrogen (BUN) blood test measures waste products circulating in the blood. Normal levels range from 7%-20 mg/dL. The less well the kidney is working, the higher the BUN.
A 24-hour urine collection test will accurately measure how much urine the kidneys are producing in a day. A urinalysis can determine if protein or red blood cells are leaking into the urine indicating abnormal kidney function. A creatinine clearance test compares the amount of creatinine in a 24-hour urine sample with the amount of creatinine in the blood to determine how much blood the kidneys are filtering each minute.
Based on the results of blood and urine tests, other tests such as a CT scan, MRI, or kidney biopsy may be ordered.
Most treatment for kidney disease involves treating the underlying cause of the disease, such as controlling high blood pressure or diabetes. Diuretic medication ("water pills") may be given to help relieve fluid accumulation. Antibiotics are used to treat kidney infections. Other drugs may be given to treat specific kidney diseases.
Diet and lifestyle changes are an important part of controlling kidney disease. Obesity increases blood pressure, so losing weight can help limit kidney damage, as can stopping smoking. Reducing sodium (salt) in the diet also helps control blood pressure. In certain kinds of kidney disease, potassium is removed in abnormally large quantities by the kidneys and excreted in urine. Eating more foods such as bananas, dried beans and peas, nuts, and potatoes that are high in potassium or taking a potassium supplement pill help reverse this effect. When protein is found in the urine, some physicians recommend reducing the amount of protein (mainly found in meat) in the diet.
When kidneys fail completely in ESRD, there are only two alternatives: dialysis or kidney transplant. There are two types of dialysis. Peritoneal dialysis uses a membrane in the individual's abdomen to filter waste products. The most common kind of peritoneal dialysis is continuous ambulatory peritoneal dialysis (CAPD), in which the individual is hooked up to a bag of dialysis fluid that he carries with him, allowing continuous dialysis. The fluid is changed four times a day. In another form of peritoneal dialysis, the abdomen is filled with dialysis fluid. Wastes filter into the fluid for several hours often while the individual is asleep, the then the fluid is drained from the body. Peritoneal dialysis can be done at home without the need for a health care professional.
In hemodialysis, the individual must go to a dialysis center about three times a week. His blood is sent through a machine that filters out the waste and then returns the cleansed blood to his body. The process takes three to four hours and is done by a health care professional.
Kidney transplants can come from either a living donor or a deceased donor. Donors are matched with recipients based on blood type and must take drugs to prevent their immune system from rejecting the kidney after transplantation. The United Network for Organ Sharing (UNOS) coordinates matching donor kidneys with appropriate recipients. As of 2005, over 100 clinical trials were enrolling patients with various types of kidney disease. Information on current clinical trials can be found at 〈http://www.clinicaltrials.gov〉.
Alternative treatments tend to focus on removing excess water from the body, but have limited effect on serious disease. Asparagus (Asparagus officinalis ) birch tea (Betula species), goldenrod infusion (Solidago species), horsetail Equisetum arvense ), and stinging nettle (Urtica dioica ) all are used to stimulate urine production.
Many individuals recover normal kidney function after developing acute kidney disease, although in some cases, such as poisoning and injury, kidney damage may be permanent. Chronic kidney disease tends to get progressively worse as the individual ages. More than 15,000 kidney transplants are done each year, and there is a often long waiting list for donated kidneys. As of 2001 (last year for which statistics were available), 80.6% of individuals receiving a transplant from a deceased donor survived for at least 5 years, and 90.4% of individuals receiving a kidney donated from a living donor survived for at least 5 years.
Maintaining a healthy body weight, getting regular exercise, and not smoking all promote kidney health. Controlling underlying diseases such as diabetes and high blood pressure are important in preventing chronic kidney diseases.
American Foundation for Urologic Disease. 1128 North Charles Street, Baltimore, MD 21201 Telephone: 800-242-2383. 〈http://www.afud.org〉.
National Kidney and Urologic Disease Clearinghouse. 3 Information Way, Bethesda, MD 20892-3580. Telephone: 800-891-5390. 〈http://www.niddk.nih.gov〉.
United Network for Organ Sharing (UNOS). P. O. Box 13770, Richmond, VA 23225. Telephone: 804-330-8500. 〈http://www.unos.org〉.
"Your Kidneys and How They Work." National Kidney and Urologic Disease Clearinghouse. July 2003 [cited 23 March 2005]. 〈http://www.kidney.niddke.nih.gov/kudiseases/pubs/yourkidneys/index.htm#rate〉.
"Kidney Disease Overview." National Kidney Disease Education Program. 9 March 2005 [cited 23 March 2005]. 〈http://www.nkdep.nih.gov/patientspublic/kindeydiseaseoverview.htm#4〉.
Congenital— Present at birth.
Diuretic— A substance that stimulates the kidney to excrete water.
Glomerulous— A twisted mass of blood capillaries and urine tubules in the kidney where filtering of waste products occurs.
Hormone— A chemical produced by living cells that travels through the circulatory system and affects tissue at some distance from where it was released.
Hypertension— High blood pressure.
Nephron— The smallest functional unit of the kidney involved in the removal of waste products and excess water from the blood.
Kidney disease refers to any condition affecting how well the kidneys work. Kidney diseases range from mild infections that can be treated with antibiotics to chronic (long-lasting) diseases that cause the kidneys to deteriorate and ultimately to stop working.
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The kidneys are a pair of bean-shaped organs located in the back of the abdominal cavity right above the waist. There is one on each side of the spinal column. The kidneys perform a number of functions, chiefly filtering the blood, removing wastes to create urine, adjusting the chemical and fluid balance in the body by controlling the concentration of urine, and participating in the control of blood pressure. The kidneys also are involved in regulating the effects of vitamin D on the body and in stimulating bone marrow to create new red blood cells. When the kidneys are damaged by disease, some or all of these functions can be impaired. When the kidneys do not function properly, a person can become very ill; when they fail to function at all, a person will die without treatment.
Kidney disease is a major health problem in the United States. Over 3.5 million Americans are affected by some form of kidney disease. Over 300,000 Americans have end-stage renal disease (ESRD), the most severe form of kidney disease. In 1996 over 12,000 people received kidney transplants. Billions of dollars are spent each year treating kidney disease.
There are three main categories of kidney diseases:
- Congenital disorder are genetic or begin very early in life.
- Chronic disorders are long-lasting and may develop gradually over many years.
- Acute disorders occur suddenly, for example from a blockage of the kidney drainage system.
What Is Dialysis?
When the kidneys stop filtering blood properly because of injury or disease, hemodialysis (hemo means blood) is the most common treatment. A dialysis machine acts as an artificial kidney. People undergoing dialysis are hooked up to the machine via needles and tubes so that the blood is pumped out of the body and through the filters in the machine. The machine does the job of the kidney in removing wastes and excess water before the blood is returned to the body through a vein. Some people need dialysis temporarily while their kidneys heal, but many more depend on it permanently to stay alive. The only alternative to dialysis for these people is a kidney transplant. In 1996 more than 180,000 people in the United States relied on dialysis.
People can be born with a kidney disorder, in which case it is called a congenital disease. For example, the two kidneys may be connected at their base to form a single horseshoe-shaped kidney. Some people have one kidney missing from birth, or two on one side, or two ureters (the tubes that carry urine from the kidney to the bladder) for one kidney. A person’s body usually can adjust to these problems because people can function with one kidney.
Mild Conditions Can Become Serious
Chronic, or long-lasting, kidney diseases are very serious conditions because they cause the kidneys to deteriorate over time. Glomerulonephritis (glom-er-u-lo-ne-FRY-tis) is a condition in which the filtering units of the kidneys called the glomeruli (glom-ER-you-li) become inflamed. It often accompanies other diseases such as diabetes* and high blood pressure, or it can develop as the result of a bacterial infection or immunologic disease.
- * diabetes
- (di-a-BEE-teez) is a disease in which the body cannot produce sufficient amounts of the hormone insulin to properly regulate the amount of sugar (glucose) in the blood.
The immune system makes proteins called antibodies to fight infection. In glomerulonephritis these antibodies become trapped in the glomeruli causing them to become inflamed. Glomerulonephritis may be treatable, or it may progress and cause severe kidney damage. Cancer, or tumors in the kidneys, also over time can stop the kidneys from functioning properly. Eventually, many of these diseases lead to end-stage renal disease (ESRD), a condition in which the kidneys shut down.
Acute Kidney Failure
Acute, or sudden, kidney failure can be caused by many things, including injury that severely reduces blood flow, severe dehydration, exposure to chemicals and drugs that are poisonous to the kidneys, infections, tumors, and kidney stones.
Pyelonephritis (PY-el-o-ne-FRY-tis), or infection of the kidney, is a common type of acute kidney disease. Its symptoms can include pain in the back or abdomen, fever, and frequent or painful urination. It can be treated effectively with antibiotics. Another well known condition is kidney stones. Kidney stones are hard crystals made of chemicals that separate from the urine and build up in the kidney. Small kidney stones can pass out of the body on their own, but larger stones require a procedure that breaks them into smaller pieces so that they can leave the body in the urine. People may recover from these kidney diseases without permanent damage to the kidneys. However, if left untreated, these diseases can cause permanent damage and kidney failure.
Disorders that affect the proper functioning of the kidneys may be diagnosed by a number of methods: blood tests, urinalysis, kidney imaging (such as x-rays and MRI scans*), and renal (kidney) biopsy (taking a sample of tissues). These tests are used to determine the type and extent of kidney disease.
How kidney disease is treated depends on the underlying cause. For example, an infection might require antibiotics, but a tumor would require surgical removal. Chronic conditions can be treated with drugs to reduce symptoms when the disease cannot be cured. A restricted diet also may help alleviate symptoms. Complete kidney failure requires dialysis two or three times a week or a kidney transplant.
Bock, Glenn H. A Parent’s Guide to Kidney Disorders. Minneapolis: University of Minnesota Press, 1993.
U.S. National Kidney and Urologic Diseases Information Clearinghouse, 3 Information Way, Bethesda, MD 20892-3580. http://www.niddk.nih.gov/health/kidney