The number of children and adolescents receiving a diagnosis of attention-deficit/hyperactivity disorder (ADHD) and prescribed medication for it has increased worldwide in recent years. Some data indicates a prevalence of up to 15% in the United States. While the specific etiology of ADHD is still unclear, it is believed to result from a combination of genetic and environmental factors.
In some cases, however, an ADHD diagnosis could be due to a slight age difference, according to a new study from the Journal of Pediatrics. In the first study to investigate the influence of relative age on ADHD diagnosis and treatment in an Asian country, researchers in Taiwan analyzed data from 378 881 randomly selected subjects aged 4–17 years to determine the rates at which they were diagnosed with ADHD or prescribed ADHD medication. The data was obtained from the Taiwan National Health Insurance Research Database.
Noting that “children and adolescents born in August are typically the youngest in their grades” because of Taiwan’s cut-off birth date of August 31 for school entry, the researchers examined the “likelihood of receiving ADHD diagnosis and treatment for those who were born in August (the youngest) compared with those who were born in September (the oldest),” they wrote.
They hypothesized that the youngest students would be more likely to receive an ADHD diagnosis and medication than the older students. The study period lasted from the beginning of September 1997 through the end of August 2011, and participants were followed until their 18th birthday or until the study period ended. The prevalence of subjects receiving a diagnosis of ADHD and a related prescription for methylphenidate or atomoxetine was examined monthly.
After adjusting for demographic variables including sex, level of urbanization, and income-related insured amount, their findings show that girls and boys born in August were 63% more likely to be diagnosed with ADHD than those born in September, and they were 76% more likely to be prescribed ADHD medication. Further analysis revealed that the increased risk of an ADHD diagnosis based on birth month applied to children in preschool and elementary school but not adolescents, and the influence of birth month on ADHD treatment was less pronounced in adolescents, suggesting that the relative-age influence may diminish as children mature.
These findings are in line with previous studies from the United States, Canada, Sweden, and Spain that found an influence of relative age on ADHD diagnosis and treatment. “Relative age, as an indicator of neurocognitive maturity, is crucial in the risk of being diagnosed with ADHD and receiving ADHD medication among children and adolescents,” the authors wrote. “Our findings also remind clinicians of the potential harm of overdiagnosis and overprescribing and emphasize the importance of considering the age of a child within a grade when diagnosing ADHD and prescribing medication to treat ADHD,” they concluded.
Chen MH, Lan WH, Bai YM, et al. Influence of Relative Age on Diagnosis and Treatment of ADHD in Taiwanese Children. J Pediatr. 2016; DOI 10.1016/j.jpeds.2016.02.012.