By Serena Gordon
WEDNESDAY, Nov. 28, 2018 (HealthDay News) -- Does being the youngest in the class up your child's odds of being erroneously diagnosed with attention deficit hyperactivity disorder (ADHD)?
It might. New research suggests these kids appear to be about 30 percent more likely to receive a diagnosis of ADHD. However, it probably doesn't change a child's actual risk of developing ADHD.
So if your child was an August baby and your school district has a Sept. 1 birth date cutoff for school admissions, your child will be one of the youngest in class. And, particularly in the early grades, those age gaps can make a big difference in behavior, researchers said.
"Physicians should take into account a child's age relative to their peers. Behavior that is normal for a child's age may appear anomalous when compared to older peers," explained study author Timothy Layton, an assistant professor of health care policy at Harvard Medical School.
The consequences from not factoring in age might be overdiagnosis and overtreatment of the disorder, according to Layton. He noted that kids born in August (in areas with a September birthday cutoff) were also more likely to be given medication for ADHD symptoms.
ADHD is a neurodevelopmental disorder that's common in children, but it may not always last into adulthood, according to the U.S. Centers for Disease Control and Prevention. Kids with ADHD may have trouble controlling their behavior, may act impulsively and may be overly active, the CDC says.
ADHD rates have been rising sharply among America's youth. Over the past two decades, the rate of ADHD jumped from 6 percent to 10 percent, according to a recent study from the University of Iowa.
In children between ages 2 and 5, the rate of ADHD diagnosis went up by 50 percent between 2007 and 2012, according to background information from the study. In 2016, more than 5 percent of U.S. children were being treated with medication for ADHD.
There's no single test that can diagnose ADHD, the CDC says. Instead, doctors must rely on a medical exam, along with information from parents, teachers and, sometimes, the child. Doctors have to rule out other disorders that can cause symptoms similar to ADHD.
To see how a child's birth date might affect the risk of being diagnosed with ADHD, the researchers reviewed data from a large insurance database with information on more than 400,000 youngsters from 50 states. The kids were born between 2007 and 2009, and followed through 2015.
In states that had a Sept. 1 cutoff date for starting kindergarten, the researchers found that 85 out of 10,000 August-born youngsters were diagnosed with ADHD. For those born in September, the ADHD rate was 64 per 10,000 kids.
When the researchers looked at treatment for ADHD, they found that 53 out of 10,000 children born in August were getting ADHD medication, compared to 40 out of 10,000 kids born in September.
Layton said these findings would likely hold true in districts that had other cutoff dates for starting school. For example, in a school with a Dec. 1 birthday cutoff for school entry, kids born in November would probably be more likely to receive an ADHD diagnosis than kids born in December.
Dr. Andrew Adesman, chief of developmental and behavioral pediatrics at Cohen Children's Medical Center in New Hyde Park, N.Y., said, "This nicely designed study has confirmed what several other investigators have likewise demonstrated -- that the youngest children within a grade are more likely to be diagnosed with ADHD than are the oldest children in that same grade."
Adesman, who was not part of the study, said that if the researchers looked at kids closer in age in the same grade, say, just a few months apart, the differences would likely be smaller.
He said this study suggests that parents of kids who are young for their grade who have ADHD symptoms may want to consider having their child repeat a grade. This might give a child time to mature, so he or she will behave more appropriately in school.
The findings were published Nov. 28 in the New England Journal of Medicine.