Q: My 16-year-old has fainted several times over the last three or four months. We're scheduled for another appointment, but so far all of the blood tests are OK and the doctor says she checks out fine. What could be wrong?
A: Fainting in childhood and adolescence is a common problem: It is estimated that up to 15 percent of children will faint at least one time before reaching adulthood. More often than not, the fainting episodes (which we term syncope) are not associated with any serious underlying problems but nonetheless can be very scary to family and friends.
The list of things that can cause people to faint is quite long. While serious cardiovascular disease is a frequent cause of syncope in adults, it is rarely the cause in children. You are probably aware of many of the common causes: a sudden change in position, hyperventilation, being overheated or dehydrated, being sick (and having a fever) and skipping breakfast and lunch while maintaining a busy schedule.
In general, any condition that interferes with blood flow back to the heart or its normal pumping action can cause someone to faint. Children and adolescents who are anemic (that is, have a low blood count) are also prone to fainting as are those who use extreme methods to lose weight (such as using water pills).
Occasionally, it is difficult to tell whether someone has fainted or whether they have had a seizure. We assume that your daughter's physician has looked for those causes.
Recently, another cause for fainting has been identified. Typically, when someone stands for a long period of time and blood pools in the legs, sensors in the heart activate mechanisms to increase the blood flow back to the heart so as to maintain a normal blood pressure. In individuals with "neurocardiogenic" syncope, the body appears tricked into believing that this response is excessive and acts to shut it down before normal blood pressure is restored. Hence, the person faints.
Dr. Wilson is director of general pediatrics at the Johns Hopkins Children's Center; Dr. Joffe is director of adolescent medicine.