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 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.
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 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. 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.
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), 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.
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, kidney stones, renal cell cancer, 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 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 may be required to cleanse the blood mechanically and prevent complications such as congestive heart failure. 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.
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. 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, sickle-cell disease, glomerular diseases, obstructive disorders, kidney stones, the urinary tract infection pyelonephritis, and analgesic nephropathy 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, 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 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 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.
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 your doctor will perform tests to identify the cause of the problem. 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.