The kidneys produce urine and serve a number of important functions, including maintaining fluid balance and blood pressure and eliminating waste products. They are very complex and efficient filters of the blood, allowing unnecessary components to pass into the urine while returning 99 percent of the filtered fluid to the circulatory system.
The kidneys adjust to the body’s fluid needs. For example, a dehydrated individual will produce less urine, allowing the body to conserve water. The kidneys also adjust the salt and mineral composition of the blood. When a kidney is damaged, diseased, or receiving an inadequate supply of blood, it cannot carry out its filtering functions properly. When this occurs, certain components of blood such as protein, sugar, and red blood cells may leak into the urine.
Normally the clear yellow urine produced by each kidney flows continuously through a narrow, muscular tube called the ureter to the bladder, where it is stored until automatic or voluntary input from the nervous system causes it to be eliminated. This process involves simultaneous contraction of muscles within the bladder wall and relaxation of muscles (called the sphincter) at the bladder’s outlet.
Painful urination (dysuria)
Discomfort while passing urine can he caused by one of the following situations:
• Infection (see below)
• Irritation from something coming in direct
contact with the genital area, such as bubble bath
or other soapy material in the tub, new laundry
soap, creams, or lotions
• Trauma
• A foreign body in the vagina or urinary tract (see genital care and concerns)
Any time your child complains of painful urination or if you notice a distinctly abnormal color of the urine (especially a reddish tinge that could indicate that blood is present), contact your child’s physician as soon as possible. If a child is having difficulty urinating because of pain, you can help by placing her in a bathtub of warm water and allowing her to urinate there.
Kidney disease
Changes in the characteristics or amount of urine may result from a disorder of the kidney itself or from a problem in the ureter or bladder. Decreased urine production may be caused specifically by dehydration or kidney disease, or obstruction to the flow of urine. There are many types of kidney diseases, but they cause only a limited number of symptoms.
Decreased or (more rarely) increased urine production
Passage of blood, which may be visible to the naked eye or detected only by chemical tests or microscopic examination
Sugar (glucose) in the urine, which is virtually always associated with a high level of glucose in the blood (diabetes)
Increased amounts of protein in the urine, which can usually be detected by a simple chemical test in the physician’s office
Swelling of the hands, ankles, feet, scrotum, or eyelids (called edema)
Pain in the mid-back or flank area on one side of the body
Fever, which may be a sign of infection within or adjacent to a kidney
Inceased urine production (polyuria)
Inceased urine production can be a normal response if a child drinks a lot of fluid, or it can indicate are serious problem. Kidneys will produce an abnormal amount of urine for three basic reasons:
Kidney damage prevents the kidneys from concentrating urine.
The hormones that control the kidneys’ concentrating abilities are not being produced or are not functioning properly.
A disease such as diabetes causes a marked elevation of certain substances (especially glucose or blood sugar) in the bloodstream. When the concentration of glucose in blood exceeds a certain level, the kidney can no longer prevent some from spilling into the urine. This results in a higher volume of urine and can eventually lead to a substantial fluid loss in the urine (hematuria)
Seeing blood in the urine can be frightening for both parent and child. But not everything that looks red is blood. It is not uncommon to see a small amount of pinkish red, paste like material in a newborn’s diaper. This is usually caused by urate crystals that form in concentrated urine. If these are seen in a breastfed baby, it may be helpful to nurse more frequently. If you are bottle-feeding, consider giving a few ounces of water. Urate crystals will usually disappear by the second week of life.
Some foods such as beets and certain medications cause a child’s urine to change color. You should consult with your child’s physician if this occurs.
Blood in an infant’s diaper area may come from the urinary tract, from the vagina in little girls, or from the gastrointestinal tract. If you notice blood in the diaper, take the diaper with you to your physician.
Blood in the urine is sometimes clearly visible but at other times may be present in quantities so small that it can be detected only by a microscopic evaluation and/or a dipstick-a thin test strip that identifies a variety of substances in the urine. The following conditions cause red blood cells to be present in the urine, and it is important that the underlying cause be determined if at all possible:
•Urinary tract infection
•Trauma, including injuries to the kidneys or genitalia
•Kidney diseases, including hereditary kidney problems, that leak small amounts of blood into the urine
•Kidney stones
•Blood-clotting problems
•Abnormalities of immune function
•Exposure to toxic substances
•Tumor, which in children would nearly always involve the kidney rather than ureter, bladder, or external genitalia
•Vigorous exercise-running, jumping, etc.
Your physician will examine your child and ask questions to sort through these possibilities. A urine specimen will be evaluated. If a urinary tract infection does not appear to be the problem, the physician will probably do a careful evaluation of the genital area and order special blood and/or imaging tests (X-ray or ultrasound)to help determine the cause of the hematuria.
Obstruction: hydronephrosis
Malformations of any portion of the urinary system can occur during fetal development. The most common ofthese in both girls and boys is an obstruction that decreases or completely stops the flow of urine. The resulting increase in pressure causes swelling within the urinary tract. When one or both kidneys are involved, the condition is called hydronephrosis (literally, “water kidney”). Sometimes this type of obstruction can be diagnosed during pregnancy through an ultrasound. One of the first surgeries developed for preborn babies was the treatment of hydronephrosis by removing the obstruction while the kidneys still had time to grow.
Obstruction: persistent urethral valves
In boys, the urine flows through the urethra inside the penis. During fetal development, small flaps called valves stop the flow of urine. Before the baby is born, these valves normally disappear, allowing urine to pass freely. If the flaps of tissue remain after birth, they can obstruct the urine flow and cause bladder distention. One clue that a baby may have urethral valves is that the urine stream is weak and dribbling rather than forceful. (Most parents of boys have been sprayed during diaper changes, an indication that the flow of urine is not obstructed.)
Obstruction: meatal stenosis
The opening at the end of the penis through which urine passes is called the meatus. If the baby boy is circumcised at birth, the head of the penis (glands) is exposed to urine and stool in the diaper. The sensitive cells of the meatus may become irritated and heal with scar tissue, which can cause a narrowing known as meatal stenosis.If the boy’s urine stream appears narrowed – a thin, jet like stream as if coming from a nozzle – or if it deviates to one side so much that he must deliberately aim his penis to keep the urine stream within the toilet bowl, he should be examined by a physician. If meatal stenosisis severe, a urologist may perform minor surgery to dialate the meatal opening.