The study estimates that if the new diagnostic guidelines had been in place in 2008, they would have lowered the prevalence of the disorder in a nationally representative database to one in 100 children.
The most recent estimate of autism prevalence from this database, according to the U.S. Centers for Disease Control and Prevention, is one in 88 children with the diagnosis.
Researchers say it's hard to tell how quickly the new guidelines will be put into practice. But some fear this change to how the condition is diagnosed may mask true increases in the number of children who develop symptoms that have been consistent with the disorder.
"The trend in the incidence of autism spectrum disorders has been one of pretty steady increases. Whether the switch to DSM-5 would offset that yearly increase remains to be seen," said study author Matthew Maenner, an epidemiologist with the CDC.
But advocates for children with autism say the ramifications of the new guidelines go beyond research. They say they're starting to see signs that children are being reclassified under the new criteria and that some may be losing access to needed services as a result.
In May, the American Psychiatric Association published sweeping new guidelines for the diagnosis of autism spectrum disorders in its Diagnostic and Statistical Manual of Mental Disorders, or DSM-5.
In the past, children who met six of 12 possible criteria could be diagnosed with one of several related conditions including autistic disorder, childhood disintegrative disorder, pervasive developmental disorder not otherwise specified (PDD-NOS) and Asperger disorder, according to study background information.
Now, those categories have been folded into a single condition -- autism spectrum disorders. In order to be diagnosed, kids must demonstrate all of three recognized deficits in social communication, and they have to show two of four different kinds of restricted or repetitive patterns of behavior.
The new study applied the updated criteria to the medical records kept in a database of nearly 645,000 8-year-old children who are being tracked by the Autism and Developmental Disabilities Monitoring Network (ADDM).
Of the 6,577 children who were classified as having an autism spectrum disorder under the old diagnostic criteria, researchers found 5,339, or 81 percent, would have kept their diagnosis under the new guidelines.
"Most of the children who didn't make the cut, they didn't miss by a lot," Maenner said. "They only needed one additional criterion to meet the DSM-5 definition. They had four of the five."
Most kids who wouldn't have met the new definition missed because they didn't show problems with nonverbal communication, which means they didn't have trouble reading or using body language or facial expressions.
The study findings were published online Jan. 22 in the journal JAMA Psychiatry.
Researchers caution that it's still not clear how the changes will play out in the real world. Doctors, for example, could change how they look for symptoms to better fit the new criteria. It's also possible that kids who don't qualify for an autism diagnosis could receive a new designation -- something called social communication disorder.
The latter is what seems to be happening, said Michael Rosanoff, associate director of public health research at Autism Speaks, a nonprofit advocacy group.
Autism Speaks is surveying parents to find out how the changes are affecting their children. Though the results are still early, and it's not a scientifically rigorous sample, he said they are seeing indications that children are being reclassified using the new criteria.
"What we've seen from the first 600 persons participating in the survey, is that there is a percentage of individuals being asked to be re-evaluated by school districts or insurers using DSM-5 criteria," he said.
About one-third of those who were reclassified said they had lost access to services.
"Our sense, from our survey and previous studies that have been published, is that individuals who are losing their autism diagnosis are getting a diagnosis of social communication disorder. The concern is there are no clinical guidelines for how to treat social communication disorder," Rosanoff said, which means that kids who get the diagnosis may not qualify for any services to treat it.
"We're concerned about this," he said.
For more about changes to autism diagnosis in the DSM-5, visit Autism Speaks.