Getting an autism diagnosis could be more difficult in 2013 when a revised diagnostic definition goes into effect. The proposed changes may affect the proportion of individuals who qualify for a diagnosis of autism spectrum disorder, according to a study by Yale Child Study Center researchers published in the April issue of the Journal of the American Academy of Child & Adolescent Psychiatry.

The proposed changes to the diagnostic definition will be published in the fifth edition of the American Psychiatric Association's (APA) "Diagnostic and Statistical Manual of Mental Disorders (DSM-5)."

"Given the potential implications of these findings for service eligibility, our findings offer important information for consideration by the task force finalizing DSM-5 diagnostic criteria," said Yale Child Study Center director Dr. Fred Volkmar, who conducted the study with colleagues Brian Reichow and James McPartland.

Volkmar and his team performed an analysis of symptoms observed in 933 individuals evaluated for autism in the field trial for DSM-4. They found that about 25 percent of those diagnosed with classic autism and 75 percent of those with Asperger's Syndrome or pervasive developmental disorder, not otherwise specified, would not meet the new criteria for autism. The study also suggests that higher-functioning individuals may be less likely to meet the new criteria than individuals with intellectual disabilities.

Volkmar cautioned that these findings reflect analyses of a single data set and that more information will be provided by upcoming field trials overseen by the APA. He stressed that it is critical to examine the impact of proposed criteria in both clinical and research settings.

"Use of such labels, particularly in the United States, can have important implications for service," he said. "Major changes in diagnosis also pose issues for comparing results across research studies."