New autism diagnosis guidelines by the American Psychiatric Association could reduce the number of people diagnosed with the condition by about a third.

These new guidelines are the first update to autism diagnosis criteria in about 20 years, a Columbia University School of Nursing news release reported.

This new  policy could leave thousands of developmentally delayed children without the Autism Spectrum Disorder  (ASD) diagnosis they need to qualify for benefits such as "social services, medical benefits and educational support," the news release reported.

A recent study looked at how the changes in the Diagnostic and Statistical Manual of Mental Disorders (DSM) would affect those with ASD. The team found the number of individuals diagnosed with ASD would drop by 31 percent following the change. The rates of AD diagnoses would also drop by 22 percent and PDD-NOS by 70 percent.

"This study raises a concern that a medical provider diagnosing a child under the new guidelines won't find the child to be on the autism spectrum, when the same child under the old criteria might have been diagnosed with ASD," Kristine M. Kulage, MA, MPH, director of the Office of Scholarship and Research Development at Columbia Nursing, said in the news release.

The older manual separated ASD in three subgroups: "autistic disorder (AD), Asperger's disorder, and pervasive development disorder-not otherwise specified (PDD-NOS)," the news release reported.  The new manual, DSM-5, eliminates these subgroups and replaces them with a more "limited range of criteria for a diagnosis."

"We are potentially going to lose diagnosis and treatment for some of the most vulnerable kids who have developmental delays," Kulage said. "In many instances, children require a diagnosis of ASD to receive medical benefits, educational support and social services."

About one in 88 U.S. children have ASD. These children experience symptoms such as communication and social problems.