Disorders of the Kidney

Your kidneys have tremendous excess capacity to do their job. In fact, you can lose more than 50 percent of your renal (kidney) function and remain healthy. However, serious health problems occur when renal function drops to 20 percent, and either a kidney transplant or dialysis (see box on page 292) is required if renal function drops below 10 to 15 percent. Once nephrons (the filtering units of the kidneys) have been destroyed, either suddenly through injury or poisoning or gradually after years of kidney disease, they can never be regenerated or repaired.

Diabetes and hypertension (high blood pressure) are the two leading causes of kidney disease. In diabetes, blood flow through the kidneys increases, causing the kidneys to enlarge, and the excess sugar in the blood damages the glomeruli (tiny blood vessels that are part of the nephrons). High blood pressure can cause kidney disease by damaging the small blood vessels needed for filtering and reabsorption of fluids. Conversely, hypertension can result from kidney disease if blood flow through the kidneys is obstructed or slowed, resulting in the release of hormones that cause blood pressure to rise. See page 365 for more information about diabetes and page 217 for more information about hypertension.

Kidney Stones

A healthy kidney removes extra electrolytes and other minerals from the blood. Normally the chemical composition of urine and prompt urination prevent these electrolytes and minerals from forming crystals and building up on the inner surfaces of the kidney. Some crystals that form may pass through the urinary tract unnoticed. However, others may accumulate until they have formed kidney stones.

Why kidney stones form in some people and not in others remains unknown. Men, especially white men, develop kidney stones more frequently than women. Kidney stones usually develop between ages 20 and 40, and once one stone has been diagnosed, more are likely to develop. A family history of kidney stones increases the risk, as do certain disorders of the kidney and recurrent kidney infections. Other diseases (such as gout and chronic inflammatory disorders) and certain medications (such as diuretics and calcium-based antacids) also can cause kidney stones.

The warning signs of kidney stones are unmistakable. Stones that are not causing symptoms may be found by chance on an X-ray or ultrasound image. Most kidney stones can be passed through the urinary system by drinking plenty of water (2 to 3 quarts per day), and taking over-the-counter pain medication as needed. If you ever pass a kidney stone, be sure to save it for testing: knowing the composition of the stone will help your doctor determine the appropriate treatment and recommend steps to prevent future stones.

Surgery is rarely needed to remove or to break up kidney stones. However, if a stone does not pass through the ureter and blocks urine flow, or if a stone causes ongoing urinary tract infection, medical treatment will be required. Extracorporeal shockwave lithotripsy (ESWL) passes shock waves through the body until they strike the stones and reduce them to the consistency of sand so they can be excreted in the urine. Lithotripsy usually is done on an outpatient basis. The procedure is performed using either intravenous sedation or epidural (spinal) anesthesia. Some lithotripsy devices require the patient to be in a water bath during the procedure, while others require that the patient lie on a soft cushion or pad.

A procedure called percutaneous nephrolithotomy may be performed when stones are especially large or when they are in tissues that make lithotripsy

Urinary Tract

Warning Signs of Kidney Stones

Some kidney stones do not cause symptoms. Others may cause sudden, severe pain when they move into the ureter and cause an obstruction. As the stone moves toward the bladder, you may feel a strong urge to urinate, or you may feel a burning sensation. Fever and chills in addition to these symptoms may indicate a urinary tract infection. Contact your doctor immediately if you experience these symptoms:

• sudden, severe pain in your back or lower side

• fever and chills

• nausea and vomiting

• cloudy or foul-smelling urine

• a frequent need to urinate in small amounts

• a burning sensation during urination

• an inability to urinate although your bladder feels full

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Concerns ineffective. In this procedure the surgeon makes a tiny incision in the patient's back and inserts a nephroscope (a special type of viewing tube) to locate and remove the stone. For stones that are lower in the ureter, a thin, flexible viewing tube (called a ureteroscope) is passed up through the urethra and the bladder to the stone; the stone is then either removed or shattered. Both of these procedures are performed using general or epidural anesthesia, and both require either a short hospital stay or are done on an outpatient basis.

Additional kidney stones are likely to develop unless preventive measures are taken. The chemical composition of the first stone must be analyzed so the doctor can determine appropriate dietary changes and prescribe appropriate medications. Often the person is asked to collect a couple of 24-hour urine samples for analysis (see "Diagnostic Procedures," Creatinine clearance, page 298). The doctor also will advise the person to drink plenty of fluids (at least eight 8-ounce glasses per day), especially water. Additional treatment will be required if an underlying cause for the stones is diagnosed. Regular urinalysis will be important for monitoring the effectiveness of preventive measures and treatment.

Glomerular Diseases

Blood enters the kidneys through arteries that branch off inside the kidneys into tiny clusters of looping blood vessels called glomeruli. The glomerulus is part of the nephron, the basic filtering unit of the kidney. When the glomeruli are damaged, protein and, in some cases, red blood cells leak into the urine. When a certain type of protein called albumin is lost in the urine, the body is less able to remove excess fluid; the excess fluid causes edema (swelling) in the face, hands, feet, or ankles. Diseases that affect kidney function by damaging these filtering clusters of blood vessels are called glomerular diseases. When the attached renal tubules are affected, a condition known as nephrotic syndrome develops.

In glomerulonephritis, the membranous tissue in the kidney that serves as a filter becomes inflamed. In glomerulosclerosis, the tiny blood vessels that form the clusters become hardened or scarred. Signs of a glomerular disease include facial puffiness, hematuria (blood in the urine; see box on next page), or foamy urine caused by excretion of extra protein. Nephrotic syndrome is marked by very high levels of protein in the urine, low levels of protein in the blood, swelling (usually of the face, hands, or feet), and high levels of cholesterol in the blood. Blood tests, urinalysis, and other specialized tests can determine the type and the location of damage.

Glomerular diseases also can result from infection in other parts of the body, such as "strep" throat, endocarditis (inflammation of the lining of the heart), and human immunodeficiency virus (HIV) infection. Treatment varies according to the underlying cause and the tissues affected.

Hematuria

Hematuria refers to excess red blood cells in the urine. In some cases of hematuria, the urine looks normal and the blood is visible only under a microscope; this is called microscopic hematuria. In other cases, the blood is visible to the naked eye and the urine looks red or cola-colored; this is called gross hematuria. (Note that some foods and food dyes also can cause the urine to look red or brown.) Usually the causes of hematuria are not serious, but all cases should be evaluated so the doctor can determine the cause and treat it appropriately. Symptoms such as pain or fever also can provide clues to the cause of hematuria, as does the timing of the blood's appearance in the urine (at the beginning, end, or throughout urination). Possible causes of hematuria include the following:

• urinary tract infection or obstruction

enlarged prostate

• kidney stones or bladder stones

• kidney cancer or bladder cancer

• injury to the urinary tract

• overexercising

• sickle-cell disease

• certain medications (including painkillers, blood-thinning drugs, and antibiotics)

• IgA nephropathy

Urinary Tract

Kidney Failure

During acute renal failure, the kidneys may suddenly lose their ability to remove wastes, concentrate urine, and conserve water and essential nutrients. Urine production decreases or stops completely. Often there is blood in the urine. Protein waste products quickly accumulate in the blood, damaging tissues and reducing organ function throughout the body. This condition, known as uremia, can be fatal if kidney function is not restored promptly and if the blood is not filtered and cleansed. Symptoms of this toxic reaction include drowsiness, confusion, loss of appetite, nausea and vomiting, and seizures. The onset of symptoms is rapid, often occurring within days, but the condition can be reversed if diagnosed and treated quickly.

Disorders of the kidney itself also can lead to acute renal failure. These disorders include direct injury to the kidney, a urinary tract infection such as acute pyelonephritis (see page 286), kidney stones (see page 289), renal cell cancer (see "Kidney Cancer," page 293), and any obstruction of the urinary tract. Acute renal failure also can be caused by reduced blood flow, which can occur after an injury, during complicated surgery, when there is uncontrolled bleeding elsewhere in the body, following severe burns, or as a result of another serious illness. Exposure to poisons, solvents, certain medications, or a blood transfusion

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Concerns can cause injury to the kidney tubules and, in turn, acute renal failure. Severe infections, autoimmune diseases, and uncontrolled high blood pressure are other possible causes of renal failure.

Both kidney failure and its underlying cause must be treated promptly. Dialysis (see box) may be required to cleanse the blood mechanically and prevent complications such as congestive heart failure (see page 233). If you experience acute kidney failure, you will be placed on a diet that is low in protein, potassium, and sodium, and your fluid intake will be closely matched to your fluid output. You may recover adequate kidney function within 2 months, although your kidneys will not return to full normal function for much longer, perhaps a year.

Dialysis

With kidney failure, when the kidneys can no longer remove waste and excess water and acid from the blood and maintain the body's chemical balance, a person must undergo kidney dialysis. In this procedure, blood from an artery in the person's arm or leg flows through a tube and into a machine called a dialysis unit that works as an artificial kidney. The blood is filtered and cleansed in the dialysis unit and returned through another tube inserted into a vein in the same arm or leg. Usually dialysis is performed at a dialysis center (although it can be done at home) three times per week. The person can sleep, read, write, talk, or watch television during the 3 to 4 hours of each treatment.

In another type of dialysis (called peritoneal dialysis), a cleansing fluid (called dialysate) is placed in the abdomen through a permanently implanted catheter (tube) to filter and cleanse the blood. To begin treatment, the person attaches a bag containing dialysate to the catheter and allows the fluid to drip into his or her abdominal cavity. The dialysate is left inside the abdomen for several hours while it pulls out waste, excess water, sodium, potassium, and other chemicals from the blood vessels that line the abdominal cavity. The fluid and waste are then drained from the abdomen through the catheter and back into the bag. The procedure is repeated four or five times per day. This method is called continuous ambulatory peritoneal dialysis and can be performed at home. Peritoneal dialysis also can be performed using a machine that fills and drains the abdominal cavity throughout the night while the person sleeps. This method is called continuous cycling peritoneal dialysis.

In chronic renal failure, the kidneys lose the same amount of function as in acute renal failure, but the loss occurs slowly over many years. The loss of kidney function is continuous and progressive and may eventually lead to end-stage renal disease (see next page). In the early stages of chronic renal failure, there are no symptoms because of the excess capacity of the kidneys to do their job. When symptoms finally appear, the damage already done is irreversible, so treatment focuses on preventing additional damage to the kidneys and slowing the progression of the disease.

Diabetes and high blood pressure are major causes of chronic renal failure. Polycystic kidney disease (see "Other Urinary Tract Disorders," page 296), sickle-cell disease (see page 239), glomerular diseases (see page 290), obstruc- 293

tive disorders, kidney stones (see page 289), the urinary tract infection Urinary pyelonephritis (see page 286), and analgesic nephropathy (see "Other Urinary Tract

Tract Disorders," page 296) all can lead to chronic renal failure.

In addition to treating the underlying cause of chronic renal failure, the doctor will take steps to prevent or treat complications that may result from limited kidney function. You may be given erythropoietin (epoetin alfa), a hormone that stimulates bone marrow to produce more red blood cells. You will be placed on a diet that is low in protein, phosphorus, potassium, sodium, and fluids to reduce the strain on your kidneys. If you continue to lose kidney function and progress to end-stage renal disease, you and your doctor will discuss your treatment options so you can make an informed decision.

End-Stage Renal Disease

People in end-stage renal disease (ESRD) have limited options. Because their kidneys have stopped working, they must have their blood cleansed by some means or they will die. They can undergo either hemodialysis or peritoneal dialysis (see previous page), or they can have a kidney transplant. Many people who have the choice will opt for transplantation because it offers a better quality of life over the long term.

Kidney transplantation succeeds in most cases. Unless they are causing high blood pressure or are frequently infected, your own kidneys usually are left in place and the new kidney is placed between them and your bladder. The surgeon connects the artery and vein of the transplanted kidney to one of your arteries and one of your veins and connects the new kidney's ureter to your bladder. The transplanted kidney may start working right away, or it may take up to a few weeks to produce urine.

The donated kidney must match your blood type and be very similar to your kidneys' tissue type. Often a blood relative (a parent, sibling, or child) can supply a kidney for transplantation. Sometimes a spouse or a friend can provide a close match. Otherwise you will need to wait for a donation from someone who has recently died but who has healthy kidneys that match yours.

The surgery will take 3 to 6 hours, and you will stay in the hospital for up to 2 weeks afterward. Your doctor will give you immunosuppressant drugs to reduce the chance of your body rejecting the new kidney. You will take these drugs for the rest of your life. If your body does not accept the new kidney, you will need to continue using dialysis until another donor kidney can be found.

Kidney Cancer

Kidney cancer is the eighth most common type of cancer among men. Twice as many men as women develop kidney cancer. The cause of this type of cancer remains unknown. Possible risk factors include smoking (which doubles the

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Concerns risk of kidney cancer), exposure to asbestos or cadmium, a family history of kidney cancer, eating a high-fat diet, being overweight, and undergoing long-term dialysis.

Different types of cancer can occur in the kidneys. The most common form of kidney cancer in adults is called renal cell cancer. As renal cell cancer grows, it may invade nearby organs, such as the liver, colon, or pancreas, or it may spread via the blood or the lymphatic system to other parts of the body, such as the lungs or the bones. A less common type of cancer, transitional cell cancer, can occur in the kidneys, but occurs more often in the bladder (see next page).

Initially renal cell cancer does not cause symptoms. As the tumor grows, however, symptoms may develop, including blood in the urine, a lump near the affected kidney, fatigue, loss of appetite, weight loss, recurrent fevers, pain in the side, and a vague feeling of being ill. If you have any of these symptoms— which could point to many of the urinary tract disorders discussed in this chap-ter—your doctor will perform tests to identify the cause of the problem (see "Diagnostic Procedures," page 297). The earlier cancer is diagnosed and treated, the better the chances for recovery.

Once cancer is detected, your doctor will want to determine whether it has spread. This will influence your treatment options. Often, all or part of the cancerous kidney is removed surgically, along with the adrenal gland and any nearby lymph nodes. If the tumor cannot be removed, the doctor may try to block blood flow to the tumor by clogging the renal artery that supplies blood to the diseased kidney; this will starve the tumor of the blood it needs. In either case, the remaining healthy kidney will do the work of both kidneys.

Radiation therapy, while not a cure, may be used to shrink large tumors or to treat metastases (cancer that has spread to other parts of the body) in the bones. Immunotherapy (treatment in which the body's immune system is stimulated to destroy cancer cells), chemotherapy (treatment with powerful anticancer drugs), and hormone therapy (treatment involving hormones that affect the growth of cancer cells) all attack the cancer at the systemic level. This means that the entire body is treated at the same time. Treating cancer at the systemic level may cause more unpleasant side effects (including nausea, vomiting, and hair loss) than other forms of treatment.

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