Protein in the urine: A concern?

My seven-year-old daughter has a problem with too much protein showing up in her urine. It first showed up two years ago during a routine physical exam. It went away for about a year and is back. Her physician says this may be something to be concerned about if it keeps showing up. Is protein in the urine common?

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Robert Steele

Robert W. Steele, MD, is a board certified pediatrician at St. John's Regional Health Center in Springfield, MO. He graduated from medical... Read more

The kidney does two important jobs in the body. It filters out the waste products in the blood so it can be released in the form of urine. It also reabsorbs those materials the body still needs which got past the original filtering system. However, there are certain things in the blood which do not get past the filtering system of the kidney simply because they are too big. The red and white blood cells are a good example. These cells are entirely too large to pass through the tiny "holes" of the filter. This is good thing because we would otherwise need a blood transfusion every time we went to the bathroom.

Proteins are large molecules which help make up our muscles, important parts of our immune system, and many other portions of our bodies. Most proteins are also too large to pass through the filtering system of the kidney. And since they are not supposed to pass into the kidney, there is no mechanism for proteins to be reabsorbed if they make it in there. Therefore, if protein is detected in the urine, it means there is something going on with the filter (called the glomerulus) that is allowing the proteins to pass.

Infections, diseases that only involve these microscopic filters, and diseases which affect the kidney as a whole are all examples of processes that might cause protein in the urine. However, a child who is otherwise growing well, not losing a very large amount of protein in the urine, and has a normal blood pressure, the most common cause of protein in the urine is called benign orthostatic proteinuria. Simply put, it means protein shows up in the urine whenever the child is standing. It causes no harm except to strike fear in concern of the parents of the children who have it.

The diagnosis of benign orthostatic proteinuria is easily made by getting a urine sample from the very first void of the morning. The night before the urine sample is to be obtained, the child completely empties his bladder and then hops right into bed. Then, the urine sample is obtained without ever standing in the morning. In other words, the urine is obtained at the bedside. If this sample has no protein in it and the child is otherwise healthy and has a normal blood pressure, the fact that the urine during the day (i.e. when he is standing) has protein in it is much less likely to be concerning.

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