The kidneys are a pair of bean-shaped organs located below the rib cage. The kidneys filter fluid and waste from the blood. The fluid that remains after filtration is urine, which flows out of the kidneys through tubes called ureters and empties into the bladder. From the bladder, urine travels through another tube, called the urethra, before it is eliminated from the body.
When functioning normally, kidneys prevent the buildup of waste in the body. They produce various hormones that help stabilize blood pressure and make red blood cells and vitamin D. But in some children, the kidneys and other parts of the urinary system don't form properly during development in the womb, causing problems with urinary and kidney function.
Having a family history of kidney or urinary tract problems can increase a child’s risk of being born with these problems. Most of the time, however, the cause of a congenital kidney or urinary tract problem is unknown.
Fortunately, most of these problems are diagnosed before birth with routine prenatal ultrasound scans. Others are first detected when a baby or child has one or more urinary tract infections. These infections may be caused by a number of conditions that alter the normal flow of urine from the kidneys to the urethra. They may also be caused by vesicoureteral reflux, in which there is a backflow of urine into the kidneys instead of flowing in a one-way direction down toward the bladder.
If not recognized early, recurrent urinary tract infections caused by an obstruction or vesicoureteral reflux can damage the kidneys, scarring kidney tissue and causing chronic kidney disease. Children with kidney disease may feel very tired and have growth problems because their kidneys can't make enough of a hormone called erythropoietin, or EPO. This hormone stimulates bone marrow, the spongy tissue in bones, to produce oxygen-carrying red blood cells.
Children with kidney disease may also develop high blood pressure, or hypertension. This is caused by a decrease in the production of a hormone called renin, which helps regulate blood pressure. As the kidneys lose their ability to filter out toxins, children may also be at risk for acidosis, a dangerous buildup of acids in the blood.
Your child’s doctor recommends a kidney and urinary tract evaluation if a routine prenatal ultrasound reveals that your unborn child has a kidney malformation or hydronephrosis. This condition causes enlargement or dilation of the renal pelvis or uppermost part of the kidney, just beyond the parts of the kidney that are responsible for filtering the urine. This can be a sign that he or she has a structural problem that is causing an obstruction in the urinary tract or vesicoureteral reflux.
Diagnosis may begin during infancy or later for children who have recurrent urinary tract infections or growth problems.
Our specialists evaluate your child’s kidneys and urinary system using the following diagnostic tests.
During a physical exam, the doctor examines your child’s abdomen to see if it is swollen or distended. Abdominal distension may be due to an obstruction or inflammation in the kidneys if there is infection. Abdominal distension may also be an indication that the bladder is not emptying completely.
The doctor may ask you if your child has experienced symptoms of a kidney or urinary tract problem, such as unexplained high fevers, listlessness, vomiting, and poor appetite. The doctor also measures your child’s growth, blood pressure, heart rate, and overall development.
If a prenatal ultrasound detects hydronephrosis, your doctor performs a kidney ultrasound—which uses sound waves to create images of structures in the body—in the first day or two after the baby is born. This imaging test is often performed in the hospital shortly after birth, but the newborn is usually dehydrated at that time.
Our doctors perform an additional ultrasound one to two weeks after the baby becomes fully hydrated, making it easier to identify any problem that requires further investigation. This test may also be performed any time your child develops a severe urinary tract infection, especially one that causes a fever.
During an ultrasound, the doctor places a handheld device called a transducer on your child’s abdomen. The transducer emits high-frequency sound waves that produce an image of the kidneys and other parts of the urinary system. The test is painless.
If the ultrasound confirms that your child has very mild hydronephrosis, the doctor may wait a few months to repeat the test. In addition, the doctor makes sure that you are aware of the signs and symptoms of a urinary tract infection, which can be difficult to recognize during the first few months of an infant’s life.
Additional tests may be required to assess the cause of the hydronephrosis and the severity of blockage or reflux. In some instances, mild to moderate hydronephrosis that develops before or shortly after birth may resolve on its own by the time your baby is 12 to 18 months old.
A urine test can determine if your child has a urinary tract infection. The doctor gives you a sterile cup to obtain a sample of your child’s urine. For babies, the doctor may place a sterile collection device over the penis or female urethra to collect a fresh urine specimen. It is usually not necessary to use a catheter—a small, flexible tube that is inserted into the bladder—to obtain a urine specimen.
The urine is tested in the doctor’s office with a special dipstick to see if it contains leukocytes, a type of white blood cell that fights bacterial infections, and nitrite, which is found in urine if certain bacteria are present. This test also measures the amount of acid, protein, and glucose (sugar) in the urine. In normally functioning kidneys, these large particles are usually filtered out and returned to the bloodstream. Elevated levels of these substances may indicate that the kidneys are not functioning properly.
A urine sample is also sent to a laboratory to confirm test results found in the doctor’s office. If the test suggests a urinary tract infection, a urine culture is performed to identify any bacteria that may be present. Urine culture results are usually available within two days, but the dipstick test provides immediate results that can help with an early diagnosis.
A voiding cystourethrogram (VCUG) is an imaging test that may be used if the doctor suspects that your child has vesicoureteral reflux or posterior urethral valves, which are extra flaps of tissue, or leaflets, that develop in the first part of the urethra below the bladder. The test is also used when a baby has one or more febrile urinary tract infections—urinary tract infections accompanied by a fever—since about half of all infants with febrile urinary tract infections have reflux.
In this test, the radiologist inserts a catheter into the urethra and injects contrast material or dye into the bladder.
X-rays, which use electromagnetic radiation to form an image of organs and other structures in the body, are taken when your child’s bladder is full and again after it has been emptied. The test is usually completed within a half hour.
A renal scan is a nuclear imaging test that compares how the two kidneys function by observing how long it takes for urine to flow from the kidneys to the bladder. The test is very effective in identifying obstructions in the urinary tract.
In this test, a radiologist injects a safe tracer substance into your child’s vein. The kidneys filter the tracer, and a special nuclear scanner is used to take pictures of the kidneys as the material travels to the bladder.
Magnetic Resonance Urography
Magnetic resonance urography (MRU) is a sophisticated imaging test that is sometimes used to obtain a more detailed picture of the urinary tract in children and evaluate its function. Instead of using X-rays, this test uses a magnetic field and radio waves to form a three-dimensional picture of the urinary system. This test is usually performed with general anesthesia, especially for younger children who are unable to remain still during the MRU.
Resources for Congenital Kidney & Urinary Tract Problems
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