by Ann Marie Dwyer

Created on: January 04, 2009   Last Updated: February 12, 2009

Autism spectrum disorders are diagnosed through a series of behavioral observations and not on traditional medical tests. Accurate autism diagnosis is based on comprehensive, professional, age-appropriate evaluations of language, behavior, social and cognitive skills. Two factors determine autism: Atypical development in socialization and communication and narrow interests or repetitive behaviors.

Understanding the symptoms and characteristics of autism, especially when contrasted against normal development, is how professionals determine whether a person has autism or an Autism Spectrum Disorder.

What is the Autism Spectrum?

Five disorders comprise Autism Spectrum Disorder: Autistic Disorder, Asperger's Disorder (sometimes called Asperger's Syndrome), Rett's Disorder, Childhood Disintegrative Disorder and Pervasive Developmental Disorder-not otherwise specified (PDD-NOS). Spectrum impairment severity is determined by how much the characteristics of the disorder affect functioning.

What is the difference?

Autistic people have problems in all three areas: Socialization, communication and restricted patterns of interest or behavior. Autism can be diagnosed in individuals with other disorders including Down's Syndrome, Fragile-X Syndrome, tuberous sclerosis and other cognitive impairments and is diagnosed in more boys than girls.

People with Asperger's only have problems in two areas: Restricted patterns of interest or behavior and socialization. Those with PDD-NOS have socialization problems and one other area: Communication or restricted interest or behavior.

Childhood Disintegrative Disorder is often confused with late-onset autism because children progress normally until age three to four and severe losses of social, communication and other skills.

Rett's Disorder primarily occurs in girls, although boys cannot be excluded. After normal development in the first months, head circumference growth slows over the next months. Purposeful hand movement is lost, and profound mental retardation is characteristic.

Prior to Testing

Before testing can begin, certain disabilities must be ruled out. Vision and hearing must be accurately checked. Since hearing impairment can inhibit appropriate development of communication, it must be ruled out in advance. Any degree of blindness will impair certain physical and cognitive skills, which can mimic some autistic difficulties.

Testing Locations

Evaluations are conducted in different environments with different professionals. By changing

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