Kidney Failure (Introduction Acute Kidney Failure Chronic Kidney Failure

Introduction

Kidney (renal) failure is the inability of the kidneys to adequately filter metabolic waste products from the blood.

Kidney failure has many possible causes. Some lead to a rapid decline in kidney function (acute kidney failure); others lead to a gradual decline in kidney function (chronic kidney failure, also called chronic kidney disease). In addition to the kidneys being unable to filter metabolic waste products (such as creatinine and urea nitrogen) from the blood, the kidneys are less able to control the amount and distribution of water in the body (fluid balance) and the levels of electrolytes (sodium, potassium, calcium, phosphate) in the blood.

When kidney failure becomes chronic, blood pressure often rises. The kidneys lose their ability to produce sufficient amounts of a hormone (erythropoietin) that stimulates the formation of new red blood cells, resulting in a low red blood cell count (anemia). In children, kidney failure affects the growth of bones. In both children and adults, kidney failure can lead to weaker, abnormal bones.

Although kidney failure can affect people of all ages, both acute and chronic kidney failure are more common in older than in younger people. Many causes of kidney failure can be treated, and kidney function may recover. The availability of dialysis has transformed kidney failure from a fatal disease to a chronic one.

Chronic Kidney Failure Chronic kidney failure (also called chronic kidney disease) is a slowly progressive (months to years) decline in the kidneys' ability to filter metabolic waste from the blood. Major causes are diabetes and high blood pressure. Blood becomes more acidic, anemia develops, nerves are damaged, bone tissue deteriorates, and risk of atherosclerosis increases. Symptoms can include urinating at night, fatigue, nausea, itching, muscle twitching and cramps, loss of sensation, confusion, difficulty breathing, and yellow skin. Diagnosis is by blood and urine tests. Treatment aims to restrict fluids, sodium, and potassium in the diet, use drugs to correct other conditions (such as diabetes, high blood pressure, anemia, and electrolyte imbalances), and, when necessary, use dialysis. Many diseases can irreversibly damage or injure the kidneys. Acute kidney failure can become chronic if kidney function does not recover after treatment. Therefore, anything that can cause acute kidney failure can cause chronic kidney failure. However, the most common cause of chronic kidney failure is diabetes mellitus, followed by high blood pressure (hypertension). Both of these conditions directly damage the kidneys' small blood vessels. Other causes of chronic kidney failure include urinary tract obstruction, kidney abnormalities (such as polycystic kidney disease and glomerulonephritis), and autoimmune disorders (such as systemic lupus erythematosus) in which antibodies damage the tiny blood vessels (glomeruli) and the tiny tubes (tubules) of the kidneys. When kidney failure is mild or moderately severe, the kidneys cannot absorb water from the urine to reduce the volume of urine and concentrate it. Later, the kidneys have less ability to excrete the acids normally produced by the body and the blood becomes more acidic, a condition called acidosis. Production of red blood cells decreases, leading to anemia. High levels of metabolic wastes in the blood can damage nerve cells in the brain, trunk, and limbs. Diseased kidneys produce hormones that increase blood pressure. In addition, diseased kidneys cannot excrete excess salt and water. Salt and water retention can lead to heart failure. The sac that surrounds the heart (pericardium) may become inflamed (pericarditis). The level of triglycerides in the blood is often elevated, which, along with high blood pressure, increases the risk for atherosclerosis. The formation and maintenance of bone tissue may be impaired (renal osteodystrophy) if certain conditions that accompany chronic kidney failure are present for a long time. These conditions include a high level of parathyroid hormone, a low concentration of calcitriol (the active form of vitamin D  ) in the blood, impaired absorption of calcium, and a high concentration of phosphate in the blood. Renal osteodystrophy may lead to bone pain and an increased risk of fractures. Symptoms Symptoms usually develop very slowly. People with mild to moderately severe kidney failure may have only mild symptoms, such as the need to urinate several times during the night (nocturia). Nocturia occurs because the kidneys cannot absorb water from the urine to reduce the volume and concentrate it as normally occurs during the night. As kidney failure progresses and metabolic wastes build up in the blood, people may feel fatigued and generally weak and may become less mentally alert. Some have a loss of appetite and shortness of breath. Anemia also contributes to fatigue and generalized weakness. The buildup of metabolic waste also causes nausea, vomiting, and an unpleasant taste in the mouth, which may lead to undernutrition and weight loss. People with chronic kidney failure tend to bruise easily or bleed for an unusually long time after cuts or other injuries. Chronic kidney failure also diminishes the body's ability to fight infections. As metabolic wastes build up to higher levels in the blood, damage to muscles and nerves can cause muscle twitches, muscle weakness, cramps, and pain. People may also feel a pins-and-needles sensation in the arms and legs and may lose sensation in certain areas of the body. Encephalopathy, a condition in which the brain malfunctions, may ensue and lead to confusion, lethargy, and seizures. Heart failure may cause shortness of breath. Pericarditis may cause chest pain and low blood pressure. People who have advanced chronic kidney failure commonly develop gastrointestinal ulcers and bleeding. The skin may turn yellow-brown, and occasionally, the concentration of urea is so high that it crystallizes from sweat, forming a white powder on the skin. Some people with chronic kidney failure itch all over their body. Their breath may also be foul. Diagnosis Blood and urine tests are essential. They confirm the presence of kidney failure and can help determine whether it is acute or chronic. In chronic kidney failure, blood levels of urea and creatinine, metabolic waste products that are normally filtered out by the kidneys, are increased. Typically, the blood becomes moderately acidic. The level of potassium in the blood is often normal or only slightly increased but can become dangerously high when kidney failure reaches an advanced stage or if people ingest large amounts of potassium or take a drug that prevents the kidneys from excreting the potassium. Usually, people have some degree of anemia. The levels of calcium and calcitriol in the blood decrease, and the phosphate and parathyroid hormone levels increase. Analysis of the urine may detect many abnormalities, including protein and abnormal cells. Ultrasonography is often done to rule out obstruction and check the size of the kidneys. Small, scarred kidneys often indicate that kidney failure is chronic. Determining a precise cause becomes increasingly difficult as kidney failure reaches an advanced stage. Removing a sample of tissue from a kidney for examination (kidney biopsy) may be the most accurate test, but it is not recommended if results of an ultrasound examination show that the kidneys are small and scarred. Prognosis Ultimately, chronic kidney failure progresses in most people regardless of treatment. The rate of decline in kidney function depends somewhat on the underlying disorder causing the kidney failure and on how well it is controlled. For example, diabetes and high blood pressure, particularly if poorly controlled, cause kidney failure to progress more rapidly. Kidney failure is fatal if not treated. Survival when kidney failure is severe (sometimes called end-stage kidney failure) is usually limited to several months in people who are not treated, but those who are treated with dialysis can live much longer. However, even with dialysis, most people with end-stage kidney failure die within 5 to 10 years. Most die from heart or blood vessel disorders or infections. Treatment Conditions that can cause or worsen kidney failure and consequences of the kidney failure that might adversely affect overall health should be treated promptly. For example, bacterial infections are treated with antibiotics, and any obstructions in the urinary tract are removed or relieved. Measures are also taken to prevent worsening of kidney function or complications of kidney failure. These measures often include Controlling diabetes, blood pressure, and cholesterol and triglyceride levels Restricting dietary protein, salt, potassium, phosphorus, and fluids Using drugs to control potassium, phosphorus, triglyceride, cholesterol, and parathyroid hormone levels and to treat heart failure or anemia Eventually, giving dialysis Controlling the level of sugar in the blood as well as high blood pressure in people with diabetes substantially slows deterioration in kidney function. Drugs called angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers may decrease the rate of decline in kidney function in some people with chronic kidney failure. However, people with severe kidney failure should not take these drugs. Meticulous attention to diet helps control several potential problems. Sometimes, mild acidosis can be controlled by increasing the intake of carbohydrates and reducing the intake of protein. However, moderate or severe acidosis may require treatment with sodium bicarbonate. The decline in kidney function can be slowed slightly by restricting the amount of protein consumed daily. People need to consume sufficient carbohydrates to offset the reduction in protein. The triglyceride and cholesterol levels may be controlled somewhat by limiting fat in the diet. Drugs such as statins, ezetimibe  , and, occasionally clofibrate or gemfibrozil  may be required to correct the levels of triglycerides, cholesterol, or both. The restriction of salt (sodium) is usually beneficial, especially if heart failure occurs. Diuretics may also relieve symptoms of heart failure, even when kidney function is poor, but dialysis may be needed to remove the excess body water in severe kidney failure. During chronic kidney failure, fluid intake may need to be restricted to prevent the sodium concentration in the blood from becoming too low. Foods that are extremely high in potassium, such as salt substitutes, must be avoided, and foods that are somewhat high in potassium, such as dates, figs, and many other fruits, should not be consumed in excess. (See the National Kidney Foundation's Fact Sheet on Potassium in the diet for more information.) A high potassium level in the blood increases the risk of abnormal heart rhythms and cardiac arrest. If the potassium level becomes too high, drugs such as sodium polystyrene sulfonate may help, but emergency dialysis may be required. The elevated phosphorus level in the blood can cause deposits of calcium and phosphorus to form in tissues, including the blood vessels. Restricting the intake of foods that are high in phosphorus, such as dairy products, liver, legumes, nuts, and most soft drinks, lowers the phosphate concentration in the blood. Drugs that bind phosphate, such as calcium carbonate  , calcium acetate, and sevelamer  , taken by mouth, may also lower the phosphorus level in the blood. Calcium citrate should be avoided. Calcium citrate is found in many calcium supplements and is in many products as a food additive (sometimes called E333). Vitamin D  and similar drugs are often taken by mouth to reduce high levels of parathyroid hormone. The anemia caused by kidney failure responds to the drugs erythropoietin  and darbepoietin. Blood transfusions are given only if the anemia is severe, is causing symptoms, and does not respond to erythropoietin  or darbepoietin. Doctors also look for and treat other causes of anemia, particularly dietary deficiencies of iron, folate (folic acid), and vitamin B12. Most people who take erythropoietin  or darbepoietin regularly need to be given iron intravenously to prevent iron deficiency, which impairs the body's response to these drugs. Anemia often requires more aggressive treatment in older people, because they are more likely to have heart disease, which can be aggravated by the anemia. The tendency to bleed can be temporarily suppressed by transfusions of fresh frozen plasma or by such drugs as desmopressin  or estrogens. Such treatment may be needed after an injury or before a surgical procedure or a tooth extraction. Doctors avoid prescribing drugs that are excreted by the kidneys, or they prescribe lower doses of such drugs. Many other drugs may need to be avoided. For example, ACE inhibitors, angiotensin II receptor blockers, and the diuretics spironolactone  andtriamterene  may need to be discontinued in people with severe kidney failure and high potassium levels because these drugs can increase potassium levels. High blood pressure is treated with antihypertensive drugs to prevent further impairment of heart and kidney function. When the treatments for chronic kidney failure are no longer effective, the only options are long-term dialysis ( see Dialysis) and kidney transplantation (see Transplantation: Kidney Transplantation). End-of-life care is important (see Death and Dying: Introduction).

Acute Kidney Failure Acute kidney failure is a rapid (days to weeks) decline in the kidneys' ability to filter metabolic waste products from the blood. Causes include disorders that decrease blood flow to the kidneys, that damage the kidneys themselves, or that block drainage of urine from the kidneys. Symptoms may include swelling, nausea, fatigue, itching, difficulty breathing, and symptoms of the disorder that caused the kidney failure. Serious complications include heart failure and high levels of potassium in the blood. Diagnosis is with blood and urine tests and usually imaging studies. Treatment involves correcting the cause of the kidney failure and sometimes doing dialysis. Acute kidney failure can result from any condition that decreases the blood supply to the kidneys, any disease affecting the kidneys themselves, or any condition that obstructs urine flow anywhere along the urinary tract. In many people, no cause of acute kidney failure can be identified. Kidney failure develops only if both kidneys are affected. Major Causes of Acute Kidney Failure Cause Underlying Problem Insufficient blood supply to the kidneys Blood loss   Loss of large amounts of sodium and fluid   Physical injury that blocks blood vessels   Inadequate pumping of the heart (heart failure)   Extremely low blood pressure (shock)   Liver failure (hepatorenal syndrome) Injury to the kidneys Blood supply to the kidneys decreased long enough to damage the kidneys   Toxic substances (for example, drugs, radiopaque dyes used in imaging tests, and poisons)   Allergic reactions (for example, to certain antibiotics)   Disorders affecting the filtering units (nephrons) of the kidneys (for example, acute glomerulonephritis, tumors damaging the kidneys, or vascular injury as occurs with hemolytic-uremic syndrome, systemic lupus erythematosus [lupus], atheroembolic kidney disease, Goodpasture's syndrome ,Wegener's granulomatosis, or polyarteritis nodosa) Obstructed urine flow Enlarged prostate   Tumor pressing on the urinary tract   Stones   Obstruction within the kidneys (for example, by stones such as oxalate or uric acid) Symptoms Symptoms depend on the severity of kidney failure, its rate of progression, and its cause. In some people, the first symptom of acute kidney failure is water retention, with swelling of the feet and ankles or puffiness of the face and hands. People may pass cola-colored urine, which may indicate a number of kidney diseases. The amount of urine (which for most healthy adults is between 3 cups [about 750 milliliters] and 2 quarts [about 2 liters] per day) often decreases to less than 2 cups (about 500 milliliters) per day or stops completely. Very little urine production is called oliguria, and no urine production is called anuria. However, some people with acute kidney failure continue to produce normal amounts of urine. As acute kidney failure persists and metabolic waste products accumulate in the body, people may experience fatigue, a decreased ability to concentrate on mental tasks, loss of appetite, nausea, and overall itchiness (pruritus). People with acute kidney failure may experience a rapid heart rate (tachycardia) and light-headedness. If the cause is an obstruction, the backup of urine within the kidneys causes the drainage system to stretch (a condition called hydronephrosis). Urinary obstruction often produces a constant dull ache under the lower ribs but may produce crampy pain—ranging from mild to excruciating—usually along the sides (flanks) of the body. Some people with hydronephrosis have blood in their urine. If the obstruction is located below the bladder, the bladder will enlarge. If the bladder enlarges rapidly, people are likely to feel severe pain in the pelvis, just above the pubic bone. If the bladder enlarges slowly, pain may be minimal, but the lower part of the abdomen may swell because of the markedly distended bladder. If acute kidney failure develops during hospitalization, the condition often relates to some recent injury, surgery, drug, or illness such as infection. The symptoms of the cause of the acute kidney failure may predominate. For example, high fever, life-threatening low blood pressure (shock), and symptoms of heart failure or liver failure may occur before symptoms of kidney failure and be more obvious and urgent. Some of the conditions that cause acute kidney failure also affect other parts of the body. For example, Goodpasture's syndrome or Wegener's granulomatosis, which damages blood vessels in the kidneys, may also damage blood vessels in the lungs, causing a person to cough up blood. Rashes are typical of some causes of acute kidney failure, including polyarteritis nodosa, systemic lupus erythematosus, and some toxic drugs. Diagnosis Blood tests that measure levels of creatinine and urea nitrogen in the blood are needed to confirm the diagnosis. A progressive daily rise in creatinine indicates acute kidney failure. The level of creatinine is also the best indicator of the degree or severity of kidney failure. The higher the level, the more severe the failure is likely to be. Other blood tests detect metabolic imbalances that occur as kidney failure persists, such as an increase in blood acidity (acidosis, which causes a low bicarbonate level), a high potassium level (hyperkalemia), a low sodium level (hyponatremia), and a high phosphorus level (hyperphosphatemia). The physical examination findings may help doctors identify the cause of the acute kidney failure. For example, enlarged or tender kidneys may indicate obstruction with hydronephrosis. Urine tests, such as a urinalysis and measurement of certain electrolytes, may enable doctors to determine whether the cause of kidney failure is insufficient blood flow to the kidneys, damage to the kidneys, or urinary obstruction. Imaging of the kidneys using ultrasonography or computed tomography (CT) is helpful, sometimes by identifying hydronephrosis or an enlarged bladder. Imaging can also reveal the size of the kidneys. X-rays of the arteries or veins that lead to and from the kidneys (angiography) may be done if obstruction of blood vessels is the suspected cause. However, angiography is done only when other tests do not provide enough information, because angiography uses radiopaque dye (contrast agent) that contains iodine, which carries a risk of additional kidney damage. Magnetic resonance imaging (MRI) can provide the same type of information. However, MRI has traditionally used gadolinium, a substance that rarely causes a disorder that triggers production of scar tissue in the body (nephrogenic fibrosing dermopathy). Thus, MRI is now less likely to be used. If other tests do not reveal the cause of kidney failure, a biopsy may be necessary to determine the diagnosis and the prognosis. Did You Know... To cause kidney failure, a disorder must affect both kidneys. Prognosis Acute kidney failure and its immediate complications, such as water retention, high acid and potassium levels in the blood, and increased urea nitrogen in the blood, can often be treated successfully. The overall survival rate is about 60%. Survival is less than 50% for people who have several organs failing at the same time. Yet, survival is about 90% for people whose kidney failure is due to decreased blood flow because body fluids have been lost through bleeding, vomiting, or diarrhea—conditions that are reversible with treatment. Treatment Any treatable cause of kidney failure is treated as soon as possible. For example, if obstruction is the cause, a catheter (a tube placed into the bladder), endoscopy, or surgery may be needed to relieve the obstruction. Often, the kidneys can heal themselves, especially if the kidney failure has existed for less than 5 days and there are no complicating problems such as infection. During this time, measures are taken to prevent kidney failure from causing serious problems. Such measures may include the following: Restricting use of certain drugs Restricting fluids, sodium, and potassium in the diet Maintaining good nutrition Giving drugs if blood levels of potassium or phosphate are too high Giving dialysis Doctors strictly limit the intake of all substances that are eliminated through the kidneys, including a large number of drugs. Salt (sodium) and potassium intake is usually restricted. Fluid intake is restricted to replacing the amount lost from the body, unless fluid is needed because there is too little blood flowing to the kidneys. Weight is measured every day because a change in weight is a good indicator of whether there is too much or too little water in the body. A healthy diet is provided to people whose condition allows them to eat. Moderate amounts of protein are acceptable, typically 0.8 to 1 grams per kilogram of body weight (0.4 to 0.5 grams per pound). Sodium polystyrene sulfonate is sometimes given by mouth or rectally to treat a high level of potassium in the blood. Calcium salts ( calcium carbonate  or calcium acetate) orsevelamer  may be given by mouth to prevent or treat a high level of phosphorus in the blood. Fluids are not restricted in people who are recovering from acute kidney failure caused by obstruction. During the recovery period, the kidneys are unable to reabsorb sodium and water normally, and a large amount of urine is produced for a period of time after the obstruction is relieved. During recovery, people may also need replacement of fluids and electrolytes, such as sodium, potassium, and magnesium. Acute kidney failure may be prolonged, necessitating removal of waste products and excess water. Waste removal can be done through dialysis, usually hemodialysis (seeDialysis: Hemodialysis). If kidney failure is predicted to be prolonged, dialysis is started as soon as possible after diagnosis. Dialysis may be needed only temporarily, until the kidneys recover their function, usually in several days to several weeks. If the kidneys are too badly damaged to recover, then the acute kidney failure becomes chronic.