Kidney Size in Children

Kidneys are central to the body's filtration of waste and production of urine. However, sometimes kidneys fail to develop properly or are impaired by diseases. This can result in abnormally small or large kidneys. These problems are usually genetic and often diagnosed before birth.

• Kidneys are central to the urinary system.

Background

• Kidneys filter waste from the blood. Each kidney has more than a million nephrons, or microscopic filters, to flush out waste products. Kidneys filter a person's entire blood supply around 400 times a day. They get rid of waste products and excess water in the body by producing urine. Kidneys also help maintain homeostasis, the body's proper balance of liquids and minerals, and produce a hormone that affects blood pressure.

Kidney Size

• Kidneys are usually about five inches long and three inches wide, approximately the size of a computer mouse. Kidney growth in children adheres to a pattern similar to the growth curves used in height. Some variation in size between the two kidneys is normal; their overall size and function is more important than the size of each individually. Kidney size is often measured through ultrasounds.

Small Kidneys

• Kidneys are considered small if they are deviate more than two standard deviations from the mean. In other words, if a child's kidney is smaller than 98 percent of the kidneys of other children his age, he is considered to have a small kidney. A small kidney can occur for several reasons. For example, a developmental defect could have been present since birth. Or the kidney could have stopped growing after an injury, such as an infection. This often causes the other kidney to grow larger than normal to compensate. This process is called compensatory hypertrophy.

Large Kidneys

• Overly large kidneys can be caused by fetal hydronephrosis. Fetal hydronephrosis can have two causes: a urinary tract obstruction or vesicoureteral reflux (VUR). VUR is the abnormal backward flow of urine from the bladder into the ureters. Fetal hydronephrosis is commonly diagnosed before a child is born. Another possible cause of large kidneys is polycystic kidney disease (PKD), a condition in which fluid-filled cysts grow on both kidneys. PKD is often inherited.

Warning Signs

• Many types of kidney disease are largely asymptomatic. However, there are several warning signs of kidney failure. First, high blood pressure could signify a kidney problem. Blood or protein in the urine may be a sign that the kidney is not filtering properly. Similarly, a blood test finding unusual levels of creatinine or blood urea nitrogen is indicative of reduced kidney function. Urination that is painful or more frequent than normal or puffiness around the eyes, hands and feet may also indicate kidney disease. Children may begin wetting the bed at night.