Early School Start Tied to Higher Risk for ADHD Diagnosis

Pauline Anderson

December 04, 2018

Children born in August in states with a September 1 cutoff for school enrollment are 30% more likely to be diagnosed with attention-deficit/hyperactivity disorder (ADHD) compared to their slightly older peers. The findings may reflect overdiagnosis of the disorder.

These results, investigators note, underscore the importance of taking into account a child's age when assessing their behavior and attention span.

"Physicians should be aware that this phenomenon exists," author Anupam B. Jena, MD, PhD, Ruth Newhouse Associate Professor, Departments of Health Care Policy and Medicine, Harvard Medical School, Boston, Massachusetts, told Medscape Medical News.

"And they should look at incorporating a child's month of birth and how old they are relative to their classmates when considering a diagnosis of ADHD," he said.

The study was published online November 28 in the New England Journal of Medicine.

Rising Rates

This is not the first time research has linked age at the time of school enrollment to a higher risk for ADHD diagnosis and treatment. But this new study is unique in that it used updated information, a large insurance database, and the researchers included data for very young children.

Rates of ADHD diagnosis and treatment are rising. Among children aged 2 to 5 years, the rate of diagnosis increased by more than 50% from 2007 to 2012.

In 2016, 5.2% of all children aged 2 to 17 years in the United States were taking medication to treat ADHD.

There are several possible reasons for this increase, said Jena. One is that there is greater awareness of the condition among healthcare providers. Another is that the diagnostic threshold may have been lowered as physicians gained more experience with ADHD.

"Doctors may be more willing to make the diagnosis now than they would have been in the past," said Jena.

Another potential factor is increased pressure on schools to measure the performance of students. In some areas, performance has been tied to funding, he said.

Birth Date a Factor

For this new study, researchers used data from the Truven Health MarketScan Research Database. This health insurance claims database contains deidentified, individual-level information from about 100 commercial payers and self-insured corporations pertaining to more than 80 million enrollees across the United States.

The cohort included 407,846 children born from 2007 through 2009 who entered kindergarten from 2012 to 2014.

There were no significant differences between August-born and September-born children or their parents.

Investigators found that the rate of ADHD diagnosis was 85.1 per 10,000 children born in August and 63.6 per 10,000 children born in September, for an absolute difference of 21.5 per 10,000 children (95% confidence interval [CI], 8.8 - 34.0).

This represents a 34% higher rate among children born in August than among children born in September.

"That tells you that 20 per 100,000 of those kids are being diagnosed with ADHD solely because they were born in August vs September," said Jena.

The difference in ADHD diagnosis rates was particularly apparent among boys. For boys born in August, the rate was higher by 32.5 per 10,000 than for boys born in September.

The rate among August-born girls was higher by 10.7 per 10,000 compared to that for girls born in September, but this difference was not significant.

However, Jena emphasized that the difference for girls was close to being significant.

When researchers compared rates of ADHD diagnoses between those born a month apart at other times during the calendar year, there was no significant difference.

Higher Treatment Rates

An advantage of this study was that researchers were able to include data regarding use of ADHD medications. They found that treatment rates were 52.9 per 10,000 children born in August and 40.4 per 10,000 children born in September, for an absolute difference of 12.5 per 10,000 children (95% CI, 2.43 - 22.4).

Among children taking ADHD medications, the average duration of treatment among children born in August was significantly longer than for those born in September (an average of 120 more days of medication).

An analysis of children younger than 4 years showed no significant difference in the ADHD diagnosis rate between those born in August and those born in September.

For states that did not use September 1 as the cutoff date for entering kindergarten, the researchers found no difference in ADHD diagnosis rates between August-born and September-born children.

The researchers also assessed rates of asthma, obesity, and diabetes, the diagnosis and treatment of which are unlikely to be affected by relative age within a school cohort. These rates did not differ between children born in August and those born in September.

"I think we did a pretty good job here of trying to demonstrate that this is a causal effect of being born in August vs September as opposed to something spurious that would explain the relationship," said Jena.

Other studies have shown a link between a child's age at school enrollment and ADHD diagnosis, but they used older data and survey reports that were vulnerable to recall bias, and it was possible that they overestimated the prevalence of ADHD.

This new study used more recent insurance claims data and focused on younger children for whom the possibility of a diagnosis of ADHD on the basis of child-to-child comparisons may be most relevant.

The authors point out that use of ADHD medications is associated with potential adverse effects, so the possibility that a child may receive medication as a result of an arbitrary cutoff date for school entry may be of interest to physicians as well as teachers and parents.

Inappropriate, Overdiagnosis?

The researchers were not able to assess the independent roles of teachers, parents, and physicians in ADHD diagnoses. But given that teachers and parents observe children in the context of their school cohort, they may be the first to determine that a child's behavior appears to be disruptive relative to that of their peers.

"At the very least, what these findings say is that we should make doctors, make teachers, make parents aware that if there's a question of an ADHD diagnosis, the month of a child's birth should be factored into the clinical assessment, and right now, it is not," said Jena.

A limitation of the study is that the researchers were unable to assess the appropriateness of an ADHD diagnosis and so could not conclude that ADHD was being overdiagnosed in children born in August relative to those born in September.

However, Jena said his "instinct" is that the results indicate overdiagnosis or inappropriate diagnosis.

He noted a study that showed that younger children in a school cohort did not perform as well as older children academically and in athletics, that fewer of them attended college, and that they were more likely to engage in juvenile criminal behavior.

"So being young for your grade can have long-term impacts," Jena said.

Another limitation of the study was that it excluded persons insured with Medicaid as well as those without insurance. As a result, for the selected group, the rate of ADHD diagnosis was lower than the national average.

Standout Study

Commenting on the study for Medscape Medical News, Steven Hinshaw, PhD, professor of psychology, University of California, Berkeley, professor of psychiatry, University of California, San Francisco, and an ADHD expert, said that during the past decade, at least four other studies had nearly identical findings, but that this new report stands out.

"The current study is convincing because of its large sample size and the use of actual insurance records of diagnosis, rather than more subjective recall," he said.

Hinshaw added that the statistical analyses used in the study "appeared to be carefully done."

However, he agreed with the authors that there is no way of knowing how the ADHD diagnoses were made. "The only data points are an insurance record that some professional made the diagnosis," he said.

He also noted that around the world, rates of ADHD diagnoses are "remarkably consistent" at about 5% to 6% of children, whereas in the United States, rates "appear to be double that."

For him, the key variable is the "quick-and-dirty" diagnosis. All too often, he said, children are labeled as having ADHD after only a brief medical visit that did not include a full developmental history or observation of behavior.

Although greater recognition of ADHD is "a good thing," cursory diagnostic practices can be problematic, said Hinshaw.

Such brief encounters can result in overdiagnosis. They can also lead to underdiagnosis if the clinician relies on an observation of the child's behavior during the short visit instead of collecting data from home and school settings.

"We certainly don't want to overpathologize and overdiagnose and overtreat children with unneeded medications," said Hinshaw. "On the other hand, with thorough, evidence-based assessments, it may be truly advantageous to identify ADHD earlier in development than later, to prevent years of lowered achievement, poor social skills, and the many later impairments that can occur — for example, substance abuse, self-harm, and accidental injury."

"Huge" Developmental Variation

Also commenting on the study for Medscape Medical News, Scott Benson, MD, a child and adolescent psychiatrist in Pensacola, Florida, said the study helps reinforce the need to be "cautious and careful" in conducting evaluations.

"We don't want to medicalize normal behavior," said Benson. "We have to recognize that there is huge developmental variation in children."

Physicians are eager to identify children with ADHD and have them undergo proper treatment, "but we want to be careful in the evaluation and make sure that we're not overdiagnosing based on age variables, based on family structure variables, and based on academic expectations," said Benson.

Benson said that when assessing a young child who is having problems at school, he wants to be sure that problems cannot be accounted for by, for example, the need for eyeglasses or the child's not being able to hear well.

He also wants to ensure that the problem does in fact interfere with classroom activity. In some cases, it does not, he said. "Sometimes I encourage parents to change schools or teachers," he added.

It's easy for clinicians to "reach for a prescription pad" instead of carrying out an adequate assessment. Conversely, Benson knows of parents who spend thousands of dollars on "overkill" assessments.

He cautioned about "pushing children harder and faster" in today's society.

Benson is not in favor of holding a disruptive child back in school. He noted that there is no scientific evidence to show that this is beneficial. It's "horribly stigmatizing" to be the "bad kid" in the class, he said.

Dr Benson and Dr Hinshaw have disclosed no relevant financial relationships.

N Engl J Med. Published online November 29, 2018. Abstract

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