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Younger relative age linked to ADHD diagnosis

Children with a younger relative age were more likely to be diagnosed with ADHD in a health service system with low prescribing rates for ADHD.

“More recently, interest has been growing in the contributory role of young relative age within the school year towards the diagnosis of ADHD. This work is important because of the potential implications for diagnostic practice and educational advice and policies,” Kapil Sayal, PhD, of University of Nottingham, U.K., and colleagues wrote. “In particular, findings of epidemiological studies from countries such as Canada, Iceland, Israel, and the U.S. — where prescribing rates for ADHD are fairly high — have shown a relative age effect, whereby younger children in a school year are more likely to be diagnosed with and treated for ADHD than are their older peers in the same school year. These findings have led to concerns that ADHD might be overdiagnosed or misdiagnosed in these countries.”

To assess associations between age within the school year and diagnosis of ADHD, researchers analyzed data from nationwide population-based registers for children born from 1991 through 2004 diagnosed with ADHD from age 7 years and onward.

Overall, 6,136 children had ADHD.

Cumulative incidence for ADHD was highest among younger children in the school year, born between September and December, compared with the oldest children in the school year, born between January and April.

ADHD incidence ratio was 1.26 (95% CI, 1.18-1.35) for boys and 1.31 (95% CI, 1.12-1.54) for girls.

The association between relative age and age at ADHD diagnosis represented children diagnosed before age 10 years. This association became stronger in more recent years, from 2004 to 2011, according to researchers.

ADHD incidence ratio was 1.37 (95% CI, 1.24-1.53) among children born between May and August and 1.64 (95% CI, 1.48-1.81) among children born between September and December, compared with children born between January and April.

Effect of relative age was not accounted for by comorbid disorders, including conduct disorder, oppositional defiant disorder and learning disorder.

“These findings suggest that key adults (teachers and parents) might interpret behavior differently of children who are younger than their classmates. When clinicians ask parents or teachers to provide information about ADHD symptoms or impairment, the informant should be asked to keep the child’s relative age in mind,” the researchers wrote. “Clinicians who are undertaking ADHD assessments or who are treating young people with a pre-existing childhood diagnosis of ADHD should also be mindful of, and perhaps consider recording, the person’s age in relation to their country’s starting age for school and cutoff date for the school year.” – by Amanda Oldt

Disclosures: The authors report no relevant financial disclosures.