The kidneys play a critical role in the body: Acting as the body's filtering system, they help control water levels and eliminate wastes through urine. They also help regulate blood pressure, red blood cell production, and the levels of calcium and minerals.

But sometimes the kidneys don't develop properly and, as a result, don't function as they should. Often these problems are genetic and not due to anything a parent did or didn't do.

Many of these problems can be diagnosed before a baby is born through routine prenatal testing and treated with medication or surgery while the child is still young. Other problems may emerge later, such as symptoms of urinary infections, growth retardation, high blood pressure, etc. In some cases, the problems are more severe and require more extensive surgical treatment.

How the Kidneys Work

The kidneys are like the body's garbage collection and disposal system. Through microscopic units called nephrons, the kidneys remove waste products and extra water from the food a person eats, returning chemicals the body needs (such as sodium, phosphorus, and potassium) back into the bloodstream. The extra water combines with other waste to become urine, which flows through thin tubes called ureters to the bladder, where it stays until it exits through the urethra (the tube that carries urine out of the body from the bladder) when someone goes to the bathroom.

The kidneys also produce three important hormones: erythropoietin, which stimulates the bone marrow to make red blood cells; renin, which helps regulate blood pressure; and the active form of vitamin D, which helps control the calcium balance in the body and maintain healthy bones.

Kidney failure, which is also called renal failure, is when the kidneys slow down or stop properly filtering wastes from the body, which can cause buildups of waste products and toxic substances in the blood. Kidney failure can be acute (which means sudden) or chronic (occurring over time and usually long lasting or permanent).

• Acute kidney injury (previously called acute kidney failure) may be due to bacterial infection, injury, shock, heart failure, poisoning, or drug overdose. Treatment includes correcting the problem that led to the kidney injury, and in some cases dialysis is required.

• Chronic kidney failure involves a deterioration of kidney function over time. In kids and teens, it can result from acute kidney failure that fails to improve, birth defects, chronic kidney diseases, or chronic severe high blood pressure. If diagnosed early, chronic kidney failure can be treated. The goal of treatment usually is to slow the decline of kidney function with medication, blood pressure control, and diet. At some point, a kidney transplant may be required.

Childhood Kidney Diseases

The most common kidney diseases in children are present at birth. They include:

Posterior urethral valve obstruction: This narrowing or obstruction of the urethra affects only boys. It can be diagnosed before the baby is born or just afterwards and treated with surgery.

Fetal hydronephrosis: This enlargement of one or both of the kidneys is caused by either an obstruction in the developing urinary tract or a condition called vesicoureteral reflux (VUR) in which urine abnormally flows backward (or refluxes) from the bladder into the ureters. Fetal hydronephrosis is usually diagnosed before the child is born and treatment varies widely. In some cases the condition only requires ongoing monitoring; in others, surgery must be done to clear the obstruction from the urinary tract.

Polycystic kidney disease (PKD): This is a condition in which many fluid-filled cysts develop in both kidneys. The cysts can multiply so much and grow so large that they lead to kidney failure. Most forms of PKD are inherited. Doctors can diagnose the condition before or after the child is born. In some cases, there are no symptoms; in others, PKD can lead to urinary tract infections, kidney stones, and high blood pressure. Treatment for PKD also varies widely. In some cases, PKD can be managed with dietary changes; in others, it requires a kidney transplant or dialysis, which is a medical treatment that helps the body filter waste when the kidneys can't do the job.

Multicystic kidney disease (MKD): This is when large cysts develop in a kidney that hasn't developed properly, eventually causing it to stop functioning. (While PKD always affects both kidneys, multicystic kidney disease usually affects only one kidney.) Fortunately, the unaffected kidney takes over and most people with MKD will have normal kidney function. MKD usually is diagnosed by prenatal ultrasound before a baby is born. Doctors manage it by monitoring blood pressure and screening for a urinary tract infection when needed. In extremely rare instances, surgical removal of the kidney may be necessary.

Renal tubular acidosis: This is a condition in which the kidneys do not properly regulate the amount of acid in the body. It can cause kidney stones and affect a child's growth, but usually can be treated with medications.

Wilms tumor: This type of childhood cancer involves the kidney, and usually is diagnosed within the first 2 years of life. It can be treated with surgery and chemotherapy.

Glomerulonephritis: This is an inflammation or infection of the glomeruli, which are parts of the nephrons that contain tiny blood vessels. It can affect the kidney's ability to properly filter out waste and can lead to swelling, blood in the urine, and a reduced amount of urine production. Some cases can be treated with medication, while others require dialysis or a kidney transplant.

Nephrotic syndrome: This occurs when the body loses large amounts of protein through the urine, typically because of some sort of change in the nephrons. It is usually diagnosed after the child is 1 year old. Swelling of the face, abdomen, and extremities are among the main symptoms, and are often relieved with medication.

Congenital problems with the urinary tract: As a child develops in the womb, a part of the urinary tract can grow to an abnormal size or in an abnormal shape or position. These problems include:

• duplication of the ureters, in which a kidney has two ureters instead of one. This can lead to urinary tract infections over time and can be treated with medication or occasionally with surgery.
• horseshoe kidney, where the two kidneys are fused (connected) into one arched kidney that usually functions normally, but is more prone to develop problems later in life. An uncomplicated horseshoe kidney does not need medical or surgical treatment, but it does need to be checked regularly by doctors.

Other Problems With the Kidneys

Sometimes a child can have other health problems that affect how well the kidneys function. These can include:

High blood pressure or hypertension. The kidneys control blood pressure by regulating the amount of salt in the body and by making the enzyme renin that, along with other substances, controls the constriction of blood vessels. The many causes of high blood pressure include any of the kidney diseases mentioned above; genetic factors such as the so-called "essential hypertension," which is the most common form of high blood pressure in adults; and obesity, which has become a major factor.

Kidney stones. The result of the build-up of crystallized salts and minerals such as calcium in the urinary tract, kidney stones (also called calculi) also can form after an infection. If kidney stones are large enough to block the kidney or ureter, they can cause severe abdominal pain. But the stones usually pass through the urinary tract on their own. In some cases, they need to be removed surgically, or treated with medication or modifications to the diet. Sometimes the first symptoms are pain and blood in the urine. Kidney stones are more common in adults than they are in kids.

Nephritis. This is any inflammation of the kidney. It can be caused by infection, an autoimmune disease (such as lupus), or an unknown reason. The first symptoms of nephritis usually are high levels of protein and blood in the urine.

Urinary tract infections (UTI). UTIs are typically caused by bacteria, such as E. coli. Most UTIs occur in the lower urinary tract, in the bladder and urethra, and they can cause pain during urination and a fever. Treatment with antibiotics should be started as soon as possible so the infection doesn't spread to the kidneys, where it can cause irreversible damage. In babies, UTIs tend to be more common in boys than girls, perhaps because boys are more affected by congenital kidney problems that predispose them to infection. Later in life, girls are more likely to get UTIs because of their shorter urethras. Bad habits can contribute to UTIs — kids holding it when they need to go to the bathroom, or wiping themselves in the wrong direction after using the toilet (they should wipe from front to back so bacteria from the stool do not get into the urethra). Among teens, girls are more likely to develop UTIs than boys, mostly due to the shorter urethra or sexual activity with a full bladder.

Symptoms of Kidney Problems

The signs and symptoms of urinary tract or kidney problems are diverse and include:

• fever
• swelling around the eyes, face, feet, and ankles (called edema)
• burning or pain during urination
• significant increase in the frequency of urination
• difficulty in controlling urination in kids who are mature enough to use the toilet
• recurrence of nighttime bedwetting (in kids who have been dry for several months)
• blood in the urine
• high blood pressure

Diagnosis of Kidney Diseases

If a kidney disease is suspected, the doctor will take a medical history, do a physical exam, and order urine tests, blood tests, imaging studies, or a biopsy to help make a diagnosis. These studies are usually suggested by a nephrologist, a doctor who specializes in the diagnosis and treatment of kidney diseases.

With urinalysis (a type of urine test), the doctor can quickly detect abnormalities (such as too many red blood cells) that may signal inflammation or irritation in the urinary tract. Urinalysis can also detect an of excess white blood cells, which is most commonly associated with bladder and kidney infections.

Certain blood tests tell doctors how well the kidneys are filtering waste products and balancing the bloodstream's chemical makeup.

Two other important diagnostic tools doctors use are blood pressure and growth measurements. Along with the heart, the kidneys are crucial to determining blood pressure. High blood pressure in a child is an important sign that the kidneys need to be evaluated. Accurate growth measurements can provide a clue to diagnosing some kidney diseases because kids with chronic kidney disease often grow poorly.

The doctor may use a kidney biopsy to evaluate kidney function. A biopsy is a procedure in which a small piece of the kidney tissue is removed with a needle. Performed while a child is under anesthesia, it's a simple procedure that can help make an accurate diagnosis of the kidney problem in about 9 out of 10 cases. It's especially helpful in the diagnosis of nephritis and nephrosis.

In addition to standard X-rays, other imaging studies a doctor may use to help diagnose kidney diseases include:

Ultrasound

The most commonly used imaging study, an ultrasound is painless and requires no X-ray exposure or special preparation. A renal ultrasound shows details of the anatomy of the kidneys and bladder. It can rule out or diagnose obstructions, developmental abnormalities, tumors, and stones in the kidneys and urinary tract.

Computerized tomography (CAT) scan

A CAT scan is often helpful in revealing the anatomy of the kidneys or bladder and, in some cases, is better than ultrasound for finding kidney stones. It can show if the kidneys have developed properly or if the flow of urine is blocked by a stone or a developmental abnormality.

Renal nuclear scan

A renal nuclear scan involves having special radioactive material injected into a vein. The radiation dose is less than that of a simple X-ray. The scan shows how the kidneys compare with each other in size, shape, and function. It also can detect scarring or other evidence of recurrent or chronic kidney infection.

Voiding cystourethrogram (VCUG)

VCUG is commonly used to evaluate the bladder and the ureters. This procedure involves putting a dye into the bladder to see whether there's an obstruction, or reflux of urine from the bladder back up to the kidneys when the child urinates.

Reviewed by: Steven Dowshen, MD
Date reviewed: November 2009
Originally reviewed by: Laszlo Hopp, MD