Published: May 3, 2007
Updated: Dec. 14, 2009
By Dennis Clements, MD, PhD
Your child’s urine tests positive for blood at school physical. You’re understandably anxious and very concerned. It is important that you understand whether this is a significant finding, so you make an appointment to find out more.
Most of the time blood in the urine is not a problem -- but occasionally it is. Dr. John Foreman, chief of the division of nephrology, tells us what to think about.
-- Dennis Clements, MD, PhD, MPH
Studies in the United States, and other parts of the world, have examined large numbers of children and have found that hematuria, the medical term for blood in the urine, is a relatively common finding.
In fact, 2 to 5 percent of school age children had tiny amounts of blood in their urine at some point in time during every day. About 1 percent of school-aged children continue to have blood in their urine when it is repeatedly tested.
While this might seem scary, most causes of hematuria are harmless. Only a very few children who continued to have hematuria had serious kidney problems. The vast majority remained perfectly healthy and the blood disappeared after a number of years.
Usually the blood cannot be seen with the naked eye and can only be detected in the laboratory using a special urine dipstick that measures blood, protein, sugar, ketones, and products from bacterial infection.
The urine dipsticks are very sensitive and turn positive with tiny amounts of blood that may be seen only when the urine is observed under the microscope (called microscopic hematuria).
Most of the time blood in the urine causes no pain to your child. Even when blood is visible to the naked eye, it is very rarely a lot of blood, so you don’t have to worry about your child losing too much blood.
Besides kidney problems, there are other causes of hematuria. The tests that your doctor may perform depend on whether there are other findings from the urine sample, such as protein, products of infection or whether there are cells during microscopic analysis. And it also matters whether your child has other constitutional symptoms such as fever or back pain.
Heavy exercise can cause microscopic hematuria is some children. Many urine exams are performed at the end of a day after gym or other physical activity and the activity itself can cause microscopic hematuria. Simply repeating the urinalysis in the morning after sleeping all night can show that the blood is no longer present.
Excess calcium in the urine (hypercalciuria) may also cause microscopic hematuria. This seems to be especially true in children who have family members with kidney stones. Doctors test for hypercalciuria by collecting all the urine for 24 hours and measuring the calcium in it. This may be detected before a kidney stone has been documented.
If a child has pain on urination (whether or not they have visible blood), then he may have a viral or bacterial bladder infection. A urine culture will be ordered which, if positive for bacteria, will help to determine antibiotic therapy. A viral urine infection will clear on its own.
If the child also has fever and back pain, then he may have a kidney infection. A kidney infection is much more serious than a simple bladder infection and implies that infection has climbed from the bladder up into the kidneys.
Other less common causes for detecting blood in the urine include:
To sort through some of these less common causes of hematuria a kidney ultrasound may be ordered to detect blockages, cysts, and tumors.
A blood test can show whether your child carries a sickle cell anemia gene and should have been performed at birth as a screening test. Blood from glomerulonephritis often is so excessive that the urine looks “cola” or “tea” colored. Typically when this occurs the blood pressure is also elevated -- another reason to perform a full exam -- to better understand the cause of hematuria.
While some of these causes of hematuria are frightening, in the vast majority of instances, once infection has been ruled out, the health care provider will not find any cause for the blood in the urine. This is called benign hematuria because it does not indicate any serious disease.
Children with benign hematuria need regular check-ups and urine testing , but about once a year is all that is necessary. Most of the time hematuria goes away without any medication, surgery, or changes in the diet.
John W. Foreman, MD, is chief of the division of nephrology at Duke University Health System.
Dennis Clements, MD, PhD, MPH, is the chief of primary care pediatrics at Duke Children's Hospital.