Study Provides Snapshot of ADHD Prevalence in U.S. Children

CINCINNATI, Sept.4 -- Almost 9% of U.S. children ages 8 to 15 meet standard diagnostic criteria for attention-deficit/hyperactivity disorder (ADHD), but less than half of them receive treatment.

Only 47.9% of the 2.4 million who met Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV) criteria for ADHD had reportedly had their conditions diagnosed by a health care professional or been treated with medication, according to a report in the September issue of the Archives of Pediatrics & Adolescent Medicine.

A research team led by Tanya E. Froehlich, M.D., of Cincinnati Children's Hospital Medical Center did a cross-sectional phone survey of the parents or caregivers of 3,082 eight- to 15-year old children who were participants in the National Health and Nutrition Examination Survey.

Survey respondents provided information about each child's ADHD symptoms between 2001 and 2004. They also provided sociodemographic information and information about whether the child had ever been diagnosed with ADHD or taken medicine to treat the disorder.

The researchers found that 8.7% (95% CI; 7.3%-10.1%) met the DSM-IV criteria for ADHD in the year before the survey took place. An additional 3.3% of children did not meet the criteria, but had a parent-reported prior diagnosis and had been treated with an ADHD medication at some point during the previous year. The latter group, however, was not included in the main analysis.

More boys than girls met the diagnostic criteria for ADHD, 11.8% versus 5.4%, respectively (P<0.001), but girls were less likely than boys to have had the disorder recognized.

There were also discrepancies in ADHD rates by race and ethnicity. Non-Hispanic white children were more likely to meet criteria for ADHD than were Mexican-American children or children of other races/ethnicities, the study showed. These findings held in both bivariate and multivariate analyses.

The study authors could not explain why Mexican-American children had lower rates of ADHD, but they speculate that this may be related to "differences in the prevalence of causal risk factors, genetic susceptibility, and/or rates of reporting ADHD symptoms across cultures."

Of the children who met the diagnostic criteria for ADHD, 38.8% had received medication to treat inattention, hyperactivity, or overactivity in the prior year and 32.0% had been taking medication for most of that year.

Regular medication use was more likely to be reported for older children than younger ones, the study showed.

Money also mattered in the new study. Children in the poorest quintile were more likely than those in the wealthiest quintile to have been diagnosed with ADHD (adjusted odds ratio [AOR] for PIR, first quintile vs fifth quintile, 2.3; 95% CI, 1.4-3.9)).

"Reasons for the increased likelihood of ADHD in poorer children may include the elevated prevalence of ADHD risk factors (i.e., premature birth and in utero or childhood exposures to toxic substances) in this group," the study authors write.

"In addition, given the high heritability of ADHD and its negative impact on social, academic and career outcomes, it is plausible that families with ADHD may cluster within the lower socioeconomic strata."

Although poor children were more likely to have ADHD, the poorest children were three to five times less likely to consistently receive medication when compared with their counterparts in other income groups, the researchers noted.

This finding "warrants further investigation and possible intervention to ensure that all children with ADHD have equitable access to treatment when appropriate," the authors conclude.

The researchers also analyzed ADHD by subtypes. Specifically, 4.4% of the children met the criteria for ADHD-1A, 2.2% for ADHD-CT and 3.0% for ADHD-HI.

The poorest children were more likely to have ADHD-HI than their wealthier counterparts (AOR for PIR, first vs fifth quintile, 3.1; 95% CI, 1.2-8.3

In addition, African Americans and Mexican Americans were less likely to have ADHD-1A, compared to their non-Hispanic white counterparts, the study showed.