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Autism is a complex neurological disorder that cannot be diagnosed through medical tests. Instead, a diagnosis is made based on the presence or absence of certain observable behaviors. Qualified and experienced professionals should perform a comprehensive evaluation to determine the presence of autism symptom and the impact that these symptoms have on an individual’s life. Because of its complexity, a diagnosis of autism should not be made after a 15 minute exam in a doctor’s office. Rather, it should only be made after an in-depth assessment process that includes the use of diagnostic instruments specifically determined to be valid for autism, along with observations of the individual in multiple settings. Additionally, since a diagnosis requires symptoms to be present prior to the age of three, a careful and detailed developmental history should be collected from a parent or caregiver.

To ensure consistency in diagnosis, professionals use standard diagnostic criteria found in the Diagnostic and Statistical Manual - 4th Edition (DSM-IV) - (1). This manual specifies the required number of symptoms needed in the three core diagnostic areas which include –socialization, communication and repetitive/restricted behaviors and interests. These symptoms must be determined to cause significant impairment in an individual’s life see Autism Fact Sheet. Finally, the manual requires professionals to ensure that other medical and/or psychological conditions are not present to account for the symptoms.

Who can diagnose?

In New York State, autism can only be diagnosed by a licensed psychologist or physician. Concerns about autism are often first mentioned to a pediatrician at a well-child visit. However, many pediatricians do not have the time or experience needed to make a diagnosis. The New York State Department of Health mandates that all physicians screen for autism at a child’s 9, 18, and 24 month visits, even in the absence of parent concerns. A positive screening should result in a referral to a specialized diagnostic clinic. Recommended screening measures include:

  • Checklist for Autism in Toddlers (CHAT) – (2)
  • Modified – Checklist for Autism in Toddlers (M-CHAT) – (3)
  • Pervasive Developmental Disorders Screening Test – (4)

Older individuals may not be referred for a diagnosis until they are in school. Families can consult the Special Education Programs in their school districts, or with their doctors for information on specialized diagnostic clinics.

What are the recommended comprehensive diagnostic measures?

A diagnosis should never be given based on the results of a screening. If a screening is positive, a comprehensive evaluation should be undertaken. Several diagnostic instruments are reliable and valid indicators of the presence or absence of autism. The instruments must be administered by specially trained evaluators and include the:

  • ADOS - Autism Diagnostic Observation Schedule – (5)
  • ADI-R - Autism Diagnostic Inventory – Revised – (6)
  • CARS - Childhood Autism Rating Scale – (7)

In addition to the use of one or more of the above measures, the evaluation should include a detailed developmental and medical history and observations of the individual in structured an natural settings.

What are recommended medical measures?

Although medical tests cannot be used to diagnose autism, they can be used to diagnose medical conditions known to cause autism (e.g, Fragile X syndrome, Tuberous Sclerosis) and medical problems that can occur with autism (e.g., seizure disorders, digestive diseases). Many physicians recommend that an individual or family undergo genetic testing if a diagnosis of autism is suspected. Other physicians recommend procedures such as EEGs or MRIs depending on the unique features of the individual. However, none of these tests are routinely useful in every case.

Hearing - It is important for an individual to be evaluated by an audiologist when autism is suspected. A hallmark symptom of autism – not responding when called – can be the result of a hearing problem. Some individuals can complete a standard hearing test in an audiologist’s office while others will require more complex testing.

Functional Behavior Assessments (FBA) - An FBA is useful with individuals who are demonstrating maladaptive or challenging behaviors. The purpose of an FBA is to determine why these behaviors occur. A plan can be developed to reduce the challenging behaviors and build new, appropriate behaviors that can serve the same function.

Specific developmental assessments - A child should be evaluated in all areas of development so that strengths and weaknesses can be identified and appropriate tretment goals can be developed. Standardized tests are often given by professionals in each area, which allow the individual’s performance to be compared to others of his/her age. In New York State these evaluations are completed at no cost to families, prior to entering the Early Intervention Program or Special Education System. Areas of assessment include:

  • Speech and language
  • Fine and gross motor skills
  • Academic skills
  • Adaptive behavior
  • Intelligence

Why is ongoing assessment important?

Once a diagnosis is made, it is important to continue the assessment process to ensure that the individual is making progress with any treatments or services they receive. A lack of progress should prompt revisions to treatment programs or plans. Substantial regressions in skill areas should prompt further medical assessments. Johnson, C.P., Myers, S.M. and the Council on Children with Disabilities (2007). Identification and evaluation of children with autism spectrum disorders. American Academy of Pediatrics Clinical Report. Pediatrics, 120 (5). 


  1. American Psychiatric Association (1994). Diagnostic and statistical manual of mental disorders: Fourth edition DSM-IV. Washington, DC: American Psychiatric Association
  2. Baron-Cohen S, Allen J, Gillberg C. Can autism be detected at 18 months? The needle, the haystack, and the CHAT. British Journal of Psychiatry. 1992;161:839–843
  3. Robins D, Fein D, Barton M, Green JA. The Modified- Checklist for Autism in Toddlers (M-CHAT): an initial investigation in the early detection of autism and pervasive developmental disorders. Journal of Autism and Developmental Disorders. 2001;31:131–144.
  4. Siegel B. The Pervasive Developmental Disorders Screening Test II (PDDST-II). San Antonio, TX: Harcourt Assessment; 2004
  5. Lord, C., Rutter, M., DiLavore, P. & Risi, S (1999) Autism Diagnostic Observation Schedule (ADOS). Western Psychological Services
  6. Couteur, Lord, C. & Rutter, M. (2003). Autism Diagnostic Interview-Revised (ADI-R). Western Psychological Services
  7. Schopler E, Reichler RJ, DeVellis RF, Daly K (1980). “Toward objective classification of childhood autism: Childhood Autism Rating Scale (CARS)”. Journal of Autism and Developmental Disorders, 10 (1): 91–103