Two years ago, the American Red Cross examined the records of nearly 2 million blood donors, including 145,000 who were 16 or 17 years old and 113,000 who were 18 or 19.

Researchers found that 11 percent of the youngest donors had an adverse reaction, as did 8 percent of the 18- to 19-year-olds. Less than 3 percent of donors aged 20 or older had complications.

Doctors say there’s probably a variety of reasons that teens are more susceptible, including the fact that they tend to be smaller than adults, and they may also have a tendency to faint from emotional stress.

But Dr. Richard Benjamin, chief medical officer of the American Red Cross, said even among teens, such reactions are rare. And the worst complications were usually just cuts and bruises from falling.

Still, given the results of the study, Benjamin said he does not want to set the age limit for donors any lower.

"The younger you are, the more likely you are to have a reaction," he said.

In Georgia, people can donate blood at age 17, or at age 16 with a parent’s consent. But different agencies have their own policies. At LifeSouth Community Blood Centers, which has a location on McEver Road in Gainesville, the age limit is 17.

LifeSouth spokeswoman Galen Unold said the organization prefers not to accept donors younger than 17, to avoid any legal issues related to informed consent.

But from a medical standpoint, she said, there’s no reason a teenager shouldn’t be able to donate blood.

"What we have found at LifeSouth is that we don’t see an increase in problems among high-school kids," she said. "The (Red Cross) survey just shocked me, because young people tend to do well after donating."

Blood collection agencies are grateful that most teens are able to donate safely, because they’re increasingly relying on that age group.

"Our future is with our younger donors," Unold said. "Ages 17 to 21 comprise about 30 percent of our total. It’s sheerly because of the opportunity."

With young folks, she explained, there’s a captive audience. Almost every high school and college holds blood drives throughout the school year. "And kids like it, because it gets them out of class."

Once people are old enough to start having careers and families of their own, Unold said, it’s tough to get them to come in and donate. But she hopes that if teens start donating blood early, it will become a habit.

"We really want kids to be donors the rest of their life," she said. "The need for blood is skyrocketing. As our population ages, there are more people with conditions such as cancer and open-heart surgery that require blood transfusions."

However, no one wants kids to donate blood if it’s going to cause them harm.

"Giving blood is a superb thing to do, and it’s something high-school students get very excited about," said Benjamin. "But we try to the best of our ability to educate students and parents in advance (about the possible risks)."

Unold, at LifeSouth, said it’s also important to educate students on what they can do to prevent bad reactions. And that starts with the most basic activities: eating and drinking.

"We insist that kids eat before they donate. A lot of them come to school without eating breakfast," she said.

Of course, donors are always offered snacks and juice after they’ve given blood. But they should also be nourished and hydrated before the procedure starts, Unold said.

A worker at the Red Cross donation center in Gainesville, who declined to be identified, said the staff is not allowed to ask donors whether they’ve had anything to eat or drink.

Dr. Ken McMilin, medical director for the Red Cross regional office in Birmingham, said donors at Red Cross centers are not required to eat if they don’t want to.

"It does help prevent complications," he said. "But it’s not an eligibility criterion. It’s up to the donor whether they want to eat beforehand."

McMilin said it’s possible the Red Cross might make policy changes as a result of the study.

"Donating is remarkably safe," he said. "But now that we have this additional data, we are looking seriously at what we can do to make donation even safer."

Benjamin said he doesn’t expect to see any changes in the minimum weight required to be a donor, which the federal Food and Drug Administration has set at 110 pounds. He said being at the lower end of the weight spectrum doesn’t seem to make donors more prone to injury.

"(In the study), the overwhelming majority of people who fell and hurt themselves were over 150 pounds," he said.

The 110-pound standard is based on blood volume. Because smaller people have less blood, taking a pint away has a greater effect, percentage-wise, than it does for larger people.

Unold said most blood donation centers do not have a scale to check a person’s weight.

"We rely on the donor to tell us the truth," she said. "At schools, if we have any doubts about a student’s weight, we can usually ask the school nurse to weigh them."

She said people who are near the minimum weight need to be careful to eat a good meal before donating.

And all donors need to take it easy after they’ve given blood.

"We make it clear that they shouldn’t do any strenuous activity until the next day," Unold said. "We work with the schools, and tell the coaches that kids (on sports teams) should not practice that day."

She urges extra caution during the summer.

"You don’t want to give blood on a hot day, then go home and mow the grass," Unold said. "Your heart has to work harder, because your blood volume has been decreased."

Benjamin said donors are always monitored for a while after they’ve given blood to make sure they don’t have a bad reaction.

But he said about half the injuries in the study occurred later in the day, after the person had already left the blood drive.