Anemia in Kidney Disease and Dialysis

What is anemia?

A person whose blood is low in red blood cells has anemia. Red blood cells carry oxygen (O₂) to tissues and organs throughout the body and enable them to use the energy from food. Without oxygen, these tissues and organs—particularly the heart and brain—may not do their jobs as well as they should. For this reason, a person who has anemia may tire easily and look pale. Anemia may also contribute to heart problems.

Anemia is common in people with kidney disease. Healthy kidneys produce a hormone called erythropoietin, or EPO, which stimulates the bone marrow to produce the proper number of red blood cells needed to carry oxygen to vital organs. Diseased kidneys, however, often don’t make enough EPO. As a result, the bone marrow makes fewer red blood cells. Other common causes of anemia include blood loss from hemodialysis and low levels of iron and folic acid. These nutrients from food help young red blood cells make hemoglobin, their main oxygen-carrying protein.

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Healthy kidneys produce a hormone called erythropoietin, or EPO, which stimulates the bone marrow to make red blood cells needed to carry oxygen throughout the body. Diseased kidneys don’t make enough EPO, and bone marrow then makes fewer red blood cells.

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What are the laboratory tests for anemia?

A complete blood count (CBC), a laboratory test performed on a sample of blood, includes a determination of a person’s hematocrit, the percentage of the blood that consists of red blood cells. The CBC also measures the amount of hemoglobin in the blood. The range of normal hematocrit and hemoglobin in women who have a period is slightly lower than for healthy men and healthy women who have stopped having periods (postmenopausal). The hemoglobin is usually about one-third the value of the hematocrit.

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When does anemia begin?

Anemia may begin to develop in the early stages of kidney disease, when you still have 20 percent to 50 percent of your normal kidney function. This partial loss of kidney function is often called chronic renal insufficiency. Anemia tends to worsen as kidney disease progresses. End-stage kidney failure, the point at which dialysis or kidney transplantation becomes necessary, doesn't occur until you have only about 10 percent of your kidney function remaining. Nearly everyone with end-stage kidney failure has anemia.

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How is anemia diagnosed?

If a person has lost at least half of normal kidney function and has a low hematocrit, the most likely cause of anemia is decreased EPO production. The estimate of kidney function, also called the glomerular filtration rate, is based on a blood test that measures creatinine. Experts recommend that doctors begin a detailed evaluation of anemia in men and postmenopausal women on dialysis when the hematocrit falls below 37 percent. For women of childbearing age, evaluation should begin when the hematocrit falls below 33 percent. The evaluation will include tests for iron deficiency and blood loss in the stool to be certain there are no other reasons for the anemia.

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How is anemia treated?

EPO

If no other cause for anemia is found, it can be treated with a genetically engineered form of EPO. The EPO is usually injected under the skin two or three times a week. Patients on hemodialysis who can’t tolerate EPO shots may receive the hormone intravenously during treatment. The intravenous method, however, requires a larger, more expensive dose and may not be as effective.

The U.S. Food and Drug Administration (FDA) recommends that patients treated with EPO therapy should achieve a target hemoglobin between 10 and 12 grams per deciliter (g/dL). Recent studies have shown that raising the hemoglobin above 12 g/dL in people who have kidney disease increases the risk of heart attack, heart failure, and stroke. People who take EPO shots should have regular tests to monitor their hemoglobin. If it climbs above 12 g/dL, their doctor should prescribe a lower dose of EPO. The FDA recommends that patients whose hemoglobin does not rise to the target level with normal doses of EPO ask their doctor to check for other causes of anemia.

Medical Tests for Prostate Problems

The prostate is a walnut-sized gland in men that produces fluid that is a component of semen. The gland has two or more lobes—or sections—enclosed by an outer layer of tissue. Located in front of the rectum and just below the bladder, where urine is stored, the prostate surrounds the urethra, which is the canal through which urine passes out of the body.

The most common prostate problem in men under 50 is inflammation or infection, which is called prostatitis. Prostate enlargement is another common problem. Because the prostate normally continues to grow as a man matures, prostate enlargement, also called benign prostatic hyperplasia or BPH, is the most common prostate problem for men over 50. Older men are at risk for prostate cancer as well, but it is much less common than BPH.

Sometimes, different prostate problems have similar symptoms. For example, one man with prostatitis and another with BPH may both have a frequent, urgent need to urinate. Other men with BPH may have different symptoms. For example, one man may have trouble beginning a stream of urine, while another may have to get up to go to the bathroom frequently at night. A man in the early stages of prostate cancer may have no symptoms at all. This confusing array of symptoms makes a thorough medical examination and testing very important. Diagnosing the problem may require a series of tests.

Male urinary tract, front and side views.

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Talking With Your Doctor or Nurse

Letting your doctor or nurse know you have a problem is the first step. Try to give as many details about the problem as you can, including when it began and how often it occurs. Tell the doctor or nurse whether you have had recurrent urinary tract infections or symptoms such as pain after ejaculation or during urination, sudden strong urges to urinate, or hesitancy and a weak urine stream. You should talk about the medicines you take, both prescription medicines and those you can buy over the counter, because they might be part of the problem. You should also talk about how much fluid you typically drink each day, whether you use caffeine or alcohol, and whether your urine has an unusual color or odor. In turn, the doctor or nurse will ask you about your general medical history, including any major illnesses or surgeries.

Other typical questions are as follows:

• Over the past month or so, how often have you had to urinate again in less than 2 hours?

• Over the past month, from the time you went to bed at night until the time you got up in the morning, how many times a night did you typically get up to urinate?

• Over the past month or so, how often have you had a sensation of not emptying your bladder completely after you finished urinating?

• Over the past month or so, how often have you had a weak urinary stream?

• Over the past month or so, how often have you had to push or strain to begin urinating?

Your answers to these questions may help your doctor or nurse identify the problem or determine what tests are needed. You may also receive a symptom score evaluation that can be used as a baseline to see how effective later treatments are at relieving those symptoms.

[Top]

Preparing for the Exam

The common tests your doctor or nurse will perform first require no special preparation. Digital rectal exams (DRE) and blood tests for prostate-specific antigen (PSA) are often included in routine physical examinations for men over 50. For African-American men and men with a family history of prostate cancer, it is recommended that tests be given starting at age 40. Some organizations even recommend that these tests be given to all men starting at age 40.

If you have urination problems or if the DRE or PSA test indicates that you might have a problem, you will probably be given additional tests that may require some preparation. Ask your doctor or nurse whether you should change your diet or fluid intake or stop taking any medications. If the tests involve inserting instruments into the urethra or rectum, you may be given antibiotics before and after the test to prevent infection.

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Procedures

DRE

This exam is usually done first. Many doctors perform a DRE as part of a routine physical exam for any man over 50, some even at 40, whether the man has urinary problems or not. You may be asked to bend over a table or to lie on your side holding your knees close to your chest. The doctor slides a gloved, lubricated finger into the rectum and feels the part of the prostate that lies next to it. You may find the DRE slightly uncomfortable, but it is very brief. This exam tells the doctor whether the gland has any bumps, irregularities, soft spots, or hard spots that require additional tests. If a prostate infection is suspected, the doctor might massage the prostate during the DRE to obtain fluid for examination with a microscope.

Digital rectal exam (DRE).

PSA Blood Test

To rule out cancer, your doctor may recommend a PSA blood test. The amount of PSA, a protein produced by prostate cells, is often higher in the blood of men who have prostate cancer. However, an elevated level of PSA does not necessarily mean you have cancer. The Food and Drug Administration has approved a PSA test for use in conjunction with a DRE to help detect prostate cancer in men age 50 or older and for monitoring men with prostate cancer after treatment. However, much remains unknown about how to interpret the PSA test, its ability to discriminate between cancer and benign prostate conditions, and the best course of action if the PSA is high.

Anemia in Kidney Disease and Dialysis

What is anemia?

A person whose blood is low in red blood cells has anemia. Red blood cells carry oxygen (O₂) to tissues and organs throughout the body and enable them to use the energy from food. Without oxygen, these tissues and organs—particularly the heart and brain—may not do their jobs as well as they should. For this reason, a person who has anemia may tire easily and look pale. Anemia may also contribute to heart problems.

Anemia is common in people with kidney disease. Healthy kidneys produce a hormone called erythropoietin, or EPO, which stimulates the bone marrow to produce the proper number of red blood cells needed to carry oxygen to vital organs. Diseased kidneys, however, often don’t make enough EPO. As a result, the bone marrow makes fewer red blood cells. Other common causes of anemia include blood loss from hemodialysis and low levels of iron and folic acid. These nutrients from food help young red blood cells make hemoglobin, their main oxygen-carrying protein.

[d]
Healthy kidneys produce a hormone called erythropoietin, or EPO, which stimulates the bone marrow to make red blood cells needed to carry oxygen throughout the body. Diseased kidneys don’t make enough EPO, and bone marrow then makes fewer red blood cells.

[Top]

What are the laboratory tests for anemia?

A complete blood count (CBC), a laboratory test performed on a sample of blood, includes a determination of a person’s hematocrit, the percentage of the blood that consists of red blood cells. The CBC also measures the amount of hemoglobin in the blood. The range of normal hematocrit and hemoglobin in women who have a period is slightly lower than for healthy men and healthy women who have stopped having periods (postmenopausal). The hemoglobin is usually about one-third the value of the hematocrit.

[Top]

When does anemia begin?

Anemia may begin to develop in the early stages of kidney disease, when you still have 20 percent to 50 percent of your normal kidney function. This partial loss of kidney function is often called chronic renal insufficiency. Anemia tends to worsen as kidney disease progresses. End-stage kidney failure, the point at which dialysis or kidney transplantation becomes necessary, doesn't occur until you have only about 10 percent of your kidney function remaining. Nearly everyone with end-stage kidney failure has anemia.

[Top]

How is anemia diagnosed?

If a person has lost at least half of normal kidney function and has a low hematocrit, the most likely cause of anemia is decreased EPO production. The estimate of kidney function, also called the glomerular filtration rate, is based on a blood test that measures creatinine. Experts recommend that doctors begin a detailed evaluation of anemia in men and postmenopausal women on dialysis when the hematocrit falls below 37 percent. For women of childbearing age, evaluation should begin when the hematocrit falls below 33 percent. The evaluation will include tests for iron deficiency and blood loss in the stool to be certain there are no other reasons for the anemia.

[Top]

How is anemia treated?

EPO

If no other cause for anemia is found, it can be treated with a genetically engineered form of EPO. The EPO is usually injected under the skin two or three times a week. Patients on hemodialysis who can’t tolerate EPO shots may receive the hormone intravenously during treatment. The intravenous method, however, requires a larger, more expensive dose and may not be as effective.

The U.S. Food and Drug Administration (FDA) recommends that patients treated with EPO therapy should achieve a target hemoglobin between 10 and 12 grams per deciliter (g/dL). Recent studies have shown that raising the hemoglobin above 12 g/dL in people who have kidney disease increases the risk of heart attack, heart failure, and stroke. People who take EPO shots should have regular tests to monitor their hemoglobin. If it climbs above 12 g/dL, their doctor should prescribe a lower dose of EPO. The FDA recommends that patients whose hemoglobin does not rise to the target level with normal doses of EPO ask their doctor to check for other causes of anemia.

Medical Tests for Prostate Problems

The prostate is a walnut-sized gland in men that produces fluid that is a component of semen. The gland has two or more lobes—or sections—enclosed by an outer layer of tissue. Located in front of the rectum and just below the bladder, where urine is stored, the prostate surrounds the urethra, which is the canal through which urine passes out of the body.

The most common prostate problem in men under 50 is inflammation or infection, which is called prostatitis. Prostate enlargement is another common problem. Because the prostate normally continues to grow as a man matures, prostate enlargement, also called benign prostatic hyperplasia or BPH, is the most common prostate problem for men over 50. Older men are at risk for prostate cancer as well, but it is much less common than BPH.

Sometimes, different prostate problems have similar symptoms. For example, one man with prostatitis and another with BPH may both have a frequent, urgent need to urinate. Other men with BPH may have different symptoms. For example, one man may have trouble beginning a stream of urine, while another may have to get up to go to the bathroom frequently at night. A man in the early stages of prostate cancer may have no symptoms at all. This confusing array of symptoms makes a thorough medical examination and testing very important. Diagnosing the problem may require a series of tests.

Male urinary tract, front and side views.

[Top]

Talking With Your Doctor or Nurse

Letting your doctor or nurse know you have a problem is the first step. Try to give as many details about the problem as you can, including when it began and how often it occurs. Tell the doctor or nurse whether you have had recurrent urinary tract infections or symptoms such as pain after ejaculation or during urination, sudden strong urges to urinate, or hesitancy and a weak urine stream. You should talk about the medicines you take, both prescription medicines and those you can buy over the counter, because they might be part of the problem. You should also talk about how much fluid you typically drink each day, whether you use caffeine or alcohol, and whether your urine has an unusual color or odor. In turn, the doctor or nurse will ask you about your general medical history, including any major illnesses or surgeries.

Other typical questions are as follows:

• Over the past month or so, how often have you had to urinate again in less than 2 hours?

• Over the past month, from the time you went to bed at night until the time you got up in the morning, how many times a night did you typically get up to urinate?

• Over the past month or so, how often have you had a sensation of not emptying your bladder completely after you finished urinating?

• Over the past month or so, how often have you had a weak urinary stream?

• Over the past month or so, how often have you had to push or strain to begin urinating?

Your answers to these questions may help your doctor or nurse identify the problem or determine what tests are needed. You may also receive a symptom score evaluation that can be used as a baseline to see how effective later treatments are at relieving those symptoms.

[Top]

Preparing for the Exam

The common tests your doctor or nurse will perform first require no special preparation. Digital rectal exams (DRE) and blood tests for prostate-specific antigen (PSA) are often included in routine physical examinations for men over 50. For African-American men and men with a family history of prostate cancer, it is recommended that tests be given starting at age 40. Some organizations even recommend that these tests be given to all men starting at age 40.

If you have urination problems or if the DRE or PSA test indicates that you might have a problem, you will probably be given additional tests that may require some preparation. Ask your doctor or nurse whether you should change your diet or fluid intake or stop taking any medications. If the tests involve inserting instruments into the urethra or rectum, you may be given antibiotics before and after the test to prevent infection.

[Top]

Procedures

DRE

This exam is usually done first. Many doctors perform a DRE as part of a routine physical exam for any man over 50, some even at 40, whether the man has urinary problems or not. You may be asked to bend over a table or to lie on your side holding your knees close to your chest. The doctor slides a gloved, lubricated finger into the rectum and feels the part of the prostate that lies next to it. You may find the DRE slightly uncomfortable, but it is very brief. This exam tells the doctor whether the gland has any bumps, irregularities, soft spots, or hard spots that require additional tests. If a prostate infection is suspected, the doctor might massage the prostate during the DRE to obtain fluid for examination with a microscope.

Digital rectal exam (DRE).

PSA Blood Test

To rule out cancer, your doctor may recommend a PSA blood test. The amount of PSA, a protein produced by prostate cells, is often higher in the blood of men who have prostate cancer. However, an elevated level of PSA does not necessarily mean you have cancer. The Food and Drug Administration has approved a PSA test for use in conjunction with a DRE to help detect prostate cancer in men age 50 or older and for monitoring men with prostate cancer after treatment. However, much remains unknown about how to interpret the PSA test, its ability to discriminate between cancer and benign prostate conditions, and the best course of action if the PSA is high.

Anemia of Inflammation and Chronic Disease

What is anemia?

Anemia is a condition in which the blood has a lower-than-normal number of red blood cells (RBCs). RBCs contain hemoglobin, an iron-rich protein that gives blood its red color and allows RBCs to transport oxygen from the lungs to the tissues of the body. Because RBC numbers are low in anemia, blood hemoglobin levels are also low.

People with anemia may feel tired because their blood does not supply enough oxygen to the body’s organs and tissues. If anemia becomes severe and prolonged, the lack of oxygen in the blood can lead to shortness of breath or exercise intolerance—a condition in which a person becomes easily fatigued during or after physical activity—and eventually cause the heart and other organs to fail.

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What is anemia of inflammation and chronic disease (AI/ACD)?

AI/ACD is a type of anemia that commonly occurs with chronic, or long-term, illnesses or infections. Cancer and inflammatory disorders, in which abnormal activation of the immune system occurs, can also cause AI/ACD. Some people develop AI/ACD without having any signs of these health problems.

AI/ACD is easily confused with iron-deficiency anemia because in both forms of anemia, levels of iron circulating in the blood are low. Circulating iron is necessary for RBC production. Low blood iron levels occur in iron-deficiency anemia because levels of iron stored in the body’s tissues are depleted. In AI/ACD, however, iron stores are normal or high. Low blood levels occur in AI/ACD, despite normal iron stores, because inflammatory and chronic diseases interfere with the body’s ability to use stored iron and absorb iron from the diet. Certain treatments for chronic diseases may also impair RBC production and contribute to AI/ACD. AI/ACD is the second most common form of anemia, after iron-deficiency anemia, but it is rarely severe.

While AI/ACD can affect people at any age, older adults are especially susceptible because they have the highest rates of chronic disease. AI/ACD is also common among hospitalized patients, particularly those with chronic illnesses.

More than 130 million Americans live with chronic conditions.¹ Addressing the causes of anemia in people with chronic conditions can help improve their health and quality of life.

¹Chronic disease overview. Centers for Disease Control and Prevention Web site. http://www.cdc.gov/nccdphp/overview.htm. Updated March 20, 2008. Accessed April 1, 2008.

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What causes AI/ACD?

A number of chronic diseases can cause anemia for different reasons.

Infectious and inflammatory diseases. As part of the immune response that occurs with infection and noninfectious inflammatory diseases, cells of the immune system release proteins called cytokines. These proteins help heal and defend the body against infection. But they can also affect normal body functions. In AI/ACD, immune cytokines interfere with the body’s ability to absorb and use iron. Cytokines may also interfere with the production and normal activity of erythropoietin (EPO), a hormone made by the kidneys that stimulates bone marrow to produce RBCs.

Infectious diseases that cause AI/ACD include tuberculosis, HIV, endocarditis—infection in the heart—and osteomyelitis, a bone infection. Sometimes acute infections—those that develop quickly and may not last long—can also cause AI/ACD.

Inflammatory diseases that can lead to AI/ACD include rheumatoid arthritis, lupus, diabetes, heart failure, degenerative joint disease, and inflammatory bowel disease (IBD). IBD, including Crohn’s disease, can also cause iron deficiency due to poor absorption of iron by the diseased intestine and bleeding from the gastrointestinal tract.

Kidney disease. People with kidney disease can develop anemia for several different reasons. For one, diseased kidneys often fail to make enough EPO. In addition, kidney disease results in abnormal absorption and use of iron, which is typical of AI/ACD. Because anemia worsens as kidney disease advances, nearly everyone with end-stage kidney disease has anemia.

People with kidney failure can also develop iron deficiency due to blood loss during hemodialysis, a procedure that removes blood from an artery, purifies it, and returns it to a vein, thereby doing the job that the kidneys no longer can. Low levels of iron and of folic acid—another nutrient required for normal RBC production—may also contribute to anemia in people with kidney disease.

Cancer. AI/ACD can occur with certain types of cancer, including Hodgkin’s disease, non-Hodgkin’s lymphoma, and breast cancer. Like chronic inflammatory disorders and infections, these types of cancer cause inflammatory cytokines to be released in the body. The anemia of AI/ACD can also be made worse by cancer chemotherapy and radiation treatments that damage the bone marrow—where RBCs are produced—and by the cancer’s invasion of bone marrow.

Anemia of Inflammation and Chronic Disease

What is anemia?

Anemia is a condition in which the blood has a lower-than-normal number of red blood cells (RBCs). RBCs contain hemoglobin, an iron-rich protein that gives blood its red color and allows RBCs to transport oxygen from the lungs to the tissues of the body. Because RBC numbers are low in anemia, blood hemoglobin levels are also low.

People with anemia may feel tired because their blood does not supply enough oxygen to the body’s organs and tissues. If anemia becomes severe and prolonged, the lack of oxygen in the blood can lead to shortness of breath or exercise intolerance—a condition in which a person becomes easily fatigued during or after physical activity—and eventually cause the heart and other organs to fail.

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What is anemia of inflammation and chronic disease (AI/ACD)?

AI/ACD is a type of anemia that commonly occurs with chronic, or long-term, illnesses or infections. Cancer and inflammatory disorders, in which abnormal activation of the immune system occurs, can also cause AI/ACD. Some people develop AI/ACD without having any signs of these health problems.

AI/ACD is easily confused with iron-deficiency anemia because in both forms of anemia, levels of iron circulating in the blood are low. Circulating iron is necessary for RBC production. Low blood iron levels occur in iron-deficiency anemia because levels of iron stored in the body’s tissues are depleted. In AI/ACD, however, iron stores are normal or high. Low blood levels occur in AI/ACD, despite normal iron stores, because inflammatory and chronic diseases interfere with the body’s ability to use stored iron and absorb iron from the diet. Certain treatments for chronic diseases may also impair RBC production and contribute to AI/ACD. AI/ACD is the second most common form of anemia, after iron-deficiency anemia, but it is rarely severe.

While AI/ACD can affect people at any age, older adults are especially susceptible because they have the highest rates of chronic disease. AI/ACD is also common among hospitalized patients, particularly those with chronic illnesses.

More than 130 million Americans live with chronic conditions.¹ Addressing the causes of anemia in people with chronic conditions can help improve their health and quality of life.

¹Chronic disease overview. Centers for Disease Control and Prevention Web site. http://www.cdc.gov/nccdphp/overview.htm. Updated March 20, 2008. Accessed April 1, 2008.

[Top]

What causes AI/ACD?

A number of chronic diseases can cause anemia for different reasons.

Infectious and inflammatory diseases. As part of the immune response that occurs with infection and noninfectious inflammatory diseases, cells of the immune system release proteins called cytokines. These proteins help heal and defend the body against infection. But they can also affect normal body functions. In AI/ACD, immune cytokines interfere with the body’s ability to absorb and use iron. Cytokines may also interfere with the production and normal activity of erythropoietin (EPO), a hormone made by the kidneys that stimulates bone marrow to produce RBCs.

Infectious diseases that cause AI/ACD include tuberculosis, HIV, endocarditis—infection in the heart—and osteomyelitis, a bone infection. Sometimes acute infections—those that develop quickly and may not last long—can also cause AI/ACD.

Inflammatory diseases that can lead to AI/ACD include rheumatoid arthritis, lupus, diabetes, heart failure, degenerative joint disease, and inflammatory bowel disease (IBD). IBD, including Crohn’s disease, can also cause iron deficiency due to poor absorption of iron by the diseased intestine and bleeding from the gastrointestinal tract.

Kidney disease. People with kidney disease can develop anemia for several different reasons. For one, diseased kidneys often fail to make enough EPO. In addition, kidney disease results in abnormal absorption and use of iron, which is typical of AI/ACD. Because anemia worsens as kidney disease advances, nearly everyone with end-stage kidney disease has anemia.

People with kidney failure can also develop iron deficiency due to blood loss during hemodialysis, a procedure that removes blood from an artery, purifies it, and returns it to a vein, thereby doing the job that the kidneys no longer can. Low levels of iron and of folic acid—another nutrient required for normal RBC production—may also contribute to anemia in people with kidney disease.

Cancer. AI/ACD can occur with certain types of cancer, including Hodgkin’s disease, non-Hodgkin’s lymphoma, and breast cancer. Like chronic inflammatory disorders and infections, these types of cancer cause inflammatory cytokines to be released in the body. The anemia of AI/ACD can also be made worse by cancer chemotherapy and radiation treatments that damage the bone marrow—where RBCs are produced—and by the cancer’s invasion of bone marrow.

Your Urinary System and How It Works

The organs, tubes, muscles, and nerves that work together to create, store, and carry urine are the urinary system. The urinary system includes two kidneys, two ureters, the bladder, two sphincter muscles, and the urethra.

How does the urinary system work?

Front view of urinary tract.

Your body takes nutrients from food and uses them to maintain all bodily functions including energy and self-repair. After your body has taken what it needs from the food, waste products are left behind in the blood and in the bowel. The urinary system works with the lungs, skin, and intestines—all of which also excrete wastes—to keep the chemicals and water in your body balanced. Adults eliminate about a quart and a half of urine each day. The amount depends on many factors, especially the amounts of fluid and food a person consumes and how much fluid is lost through sweat and breathing. Certain types of medications can also affect the amount of urine eliminated.

The urinary system removes a type of waste called urea from your blood. Urea is produced when foods containing protein, such as meat, poultry, and certain vegetables, are broken down in the body. Urea is carried in the bloodstream to the kidneys.

The kidneys are bean-shaped organs about the size of your fists. They are near the middle of the back, just below the rib cage. The kidneys remove urea from the blood through tiny filtering units called nephrons. Each nephron consists of a ball formed of small blood capillaries, called a glomerulus, and a small tube called a renal tubule. Urea, together with water and other waste substances, forms the urine as it passes through the nephrons and down the renal tubules of the kidney.

From the kidneys, urine travels down two thin tubes called ureters to the bladder. The ureters are about 8 to 10 inches long. Muscles in the ureter walls constantly tighten and relax to force urine downward away from the kidneys. If urine is allowed to stand still, or back up, a kidney infection can develop. Small amounts of urine are emptied into the bladder from the ureters about every 10 to 15 seconds.

The bladder is a hollow muscular organ shaped like a balloon. It sits in your pelvis and is held in place by ligaments attached to other organs and the pelvic bones. The bladder stores urine until you are ready to go to the bathroom to empty it. It swells into a round shape when it is full and gets smaller when empty. If the urinary system is healthy, the bladder can hold up to 16 ounces (2 cups) of urine comfortably for 2 to 5 hours.

Circular muscles called sphincters help keep urine from leaking. The sphincter muscles close tightly like a rubber band around the opening of the bladder into the urethra, the tube that allows urine to pass outside the body.

Nerves in the bladder tell you when it is time to urinate, or empty your bladder. As the bladder first fills with urine, you may notice a feeling that you need to urinate. The sensation to urinate becomes stronger as the bladder continues to fill and reaches its limit. At that point, nerves from the bladder send a message to the brain that the bladder is full, and your urge to empty your bladder intensifies.

When you urinate, the brain signals the bladder muscles to tighten, squeezing urine out of the bladder. At the same time, the brain signals the sphincter muscles to relax. As these muscles relax, urine exits the bladder through the urethra. When all the signals occur in the correct order, normal urination occurs.

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What causes problems in the urinary system?

Problems in the urinary system can be caused by aging, illness, or injury. As you get older, changes in the kidneys’ structure cause them to lose some of their ability to remove wastes from the blood. Also, the muscles in your ureters, bladder, and urethra tend to lose some of their strength. You may have more urinary infections because the bladder muscles do not tighten enough to empty your bladder completely. A decrease in strength of muscles of the sphincters and the pelvis can also cause incontinence, the unwanted leakage of urine. Illness or injury can also prevent the kidneys from filtering the blood completely or block the passage of urine.

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How are problems in the urinary system detected?

Urinalysis is a test that studies the content of urine for abnormal substances such as protein or signs of infection. This test involves urinating into a special container and leaving the sample to be studied.

Urodynamic tests evaluate the storage of urine in the bladder and the flow of urine from the bladder through the urethra. Your doctor may want to do a urodynamic test if you are having symptoms that suggest problems with the muscles or nerves of your lower urinary system and pelvis—ureters, bladder, urethra, and sphincter muscles.

Urodynamic tests measure the contraction of the bladder muscle as it fills and empties. The test is done by inserting a small tube called a catheter through your urethra into your bladder to fill it either with water or a gas. Another small tube is inserted into your rectum or vagina to measure the pressure put on your bladder when you strain or cough. Other bladder tests use x-ray dye instead of water so that x-ray pictures can be taken when the bladder fills and empties to detect any abnormalities in the shape and function of the bladder. These tests take about an hour.