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Diagnosis of Autism

  1. How is autism spectrum disorder (ASD) diagnosed?
  2. Criteria
  3. Tests
  4. In children
  5. In teens
  6. In adults
  7. Increase in diagnoses
  8. FAQs

How is autism spectrum disorder (ASD) diagnosed?

Autism, also known as autism spectrum disorder or ASD for short, is a developmental disorder that affects the way a person communicates and interacts with others, as well as their behavior and the ways in which they learn.[1]

In the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5),[2] autism spectrum disorder now covers conditions that used to be classified separately:[3]

  • Asperger syndrome
  • Autistic disorder
  • Pervasive developmental disorder not otherwise specified (PDD-NOS)
  • Childhood disintegrative disorder

A person needs to meet all DSM-5 criteria, as assessed by a trained and licensed medical professional, to receive a diagnosis of autism spectrum disorder.[2] These criteria, which include significant challenges in social functioning, are detailed below.

Diagnostic criteria for autism spectrum disorder

The criteria for the diagnosis of ASD are detailed in the DSM-5 and include the following:[4][5]

  • Persistent difficulties in social communication and social interaction in many contexts
  • At least two examples of restricted interests or repetitive behavior
  • Signs must have been present in the early years of life
  • Symptoms cause significant problems in social, working or other functioning
  • Symptoms cannot be explained by other learning or developmental disorders

A diagnosis of autism will be considered only if all of the above criteria have been met. It will typically be accompanied by an assessment of severity level, which can determine how much support a person will require.[4]

Tests used to diagnose autism

Some of the diagnostic tests that may be used to screen for autism spectrum disorder include:[5][6]

M-CHAT-R (Modified Checklist for Autism in Toddlers, Revised) CARS (Childhood Autism Rating Scale) GARS (Gilliam Autism Rating Scale) ABC (Autism Behavior Checklist) Social Communication Questionnaire ADOS (Autism Diagnostic Observation Schedule) ADI-R (Autism Diagnostic Interview-Revised)

These tests and assessments should be carried out by a licensed medical professional, who can explain what they look for and how they work. If you suspect that you or someone you know might have autism, it is recommended that you consult a doctor.

Good to know: It is not possible to formally diagnose autism in oneself or another person on one’s own, using self-assessments or checklists, though some may be helpful in increasing understanding of autism spectrum disorder, particularly among adults.[7][8] If you are concerned about any symptoms that you or a loved one may be experiencing, consider trying the Ada app for a free assessment.

Genetic testing for autism

Where there is a family history of autism spectrum disorder or physical evidence of another genetic disorder present, gene testing or chromosome analysis may be recommended as part of the diagnostic process. Genetic testing and counseling may provide helpful information to the person’s family, both about the condition itself and possible risks that may exist for relatives. However, it is not clear whether such testing has an effect on a person’s health outcomes.[6][9][10]

Good to know: Genetic testing is also sometimes recommended for children who have been newly diagnosed with autism spectrum disorder.[10]

Diagnosing autism in young children

Some children with autism spectrum disorder display signs within the first few months, others after 24 months (two years) old. Up to 90 percent of children with autism display signs before two years of age, but most are diagnosed between the ages of three and five years. Some children may initially develop according to normal patterns but then stop developing around 18 to 24 months or lose skills they had already developed.[3]

It may be helpful to keep a diary of behaviors, habits and incidents about a child with suspected autism. In the case of incidents, it may be helpful to record what happened and where, as well as anything notable that occured beforehand.[11]

Screening for autism

The American Academy of Pediatrics recommends reviewing children’s development at all early years health checks and screening specifically for autism spectrum disorder at the 18-month and 24-month checks.[12]

If autism spectrum disorder is suspected, other medical professionals will carry out an assessment. These can include a:[13][14]

Developmental pediatrician Psychologist Neurologist Speech therapist

Blood and hearing tests, as well as an EEG, may also be carried out to eliminate other potential causes for the symptoms, including:[15][16][14]

Genetic disorders which can affect development Lead poisoning, which can can cause developmental and behavioral problems Hearing difficulties, which may explain a lack of response

Diagnosing autism in older children and teenagers

Children with less severe forms of autism spectrum disorder may find their symptoms first becoming noticeable at school. For example, a child may find it difficult to form friendships and to recognize social cues or linguistic phenomena like sarcasm or jokes.[14]

Schools will often communicate with parents or carers and may perform an initial evaluation or recommend visiting a health professional, such as a psychologist.

Diagnosis of autism in adults

Some people do not receive a diagnosis of autism spectrum disorder until adulthood. This can be due to complicating factors such as the person being on the higher functioning end of the autism spectrum, having other disorders or being misdiagnosed, for example with one of the following:[17][18]

If signs of autism are suspected in an adult, a doctor should refer the person to a psychologist, psychiatrist or neuropsychologist who has experience with autism spectrum disorder. A diagnosis of autism may be reached after taking a history of the person’s life and interaction with others, as well as potentially talking to family members who may remember details of the person’s early development.[14]

A diagnosis of autism as an adult can provide the person with an explanation for previous difficulties and offer the opportunity for self-understanding and access to services. As it is not possible to formally diagnose autism in oneself or another person on one’s own, seeing a health professional is important if the disorder is suspected.

Increase in autism diagnoses

More people are being diagnosed with autism spectrum disorder. However, a variety of factors may be affecting the rate of this increase, including:

  • More awareness of autism among caregivers and affected people, leading to more referrals
  • Broader diagnostic criteria
  • Better awareness of diagnostic criteria among medical professionals

There may also be a genuine increase in the number of people with autism. However, at present, it is unclear what is behind the statistics.[19]

Autism diagnosis FAQs

Q: What is the average age of autism diagnosis?
A: Most children with ASD are diagnosed between three and five years old. However, diagnosis is possible in younger children, with the majority of those with autism showing signs before the age of two, and screening is recommended as part of a child’s 18-month and 24-month health checks. For children with Asperger’s syndrome, the average age of diagnosis seems to be closer to seven.[3][12][20][21] Some people are not diagnosed with autism spectrum disorder until later in life, when they are teenagers or adults.

Q: Can an autism diagnosis be wrong?
A: It is possible for a person to be misdiagnosed with autism or another developmental disorder or mental health condition. However, as licensed health professionals use strict criteria for diagnosis, this is not considered to be very likely. If a person is concerned about a diagnosis, they can request a second opinion from another professional.

Q: Where does one get an autism diagnosis?
A: Only a licensed medical practitioner can diagnose a person with autism spectrum disorder. Typically, this will require referral to a specialist. It is not possible to diagnose autism yourself. If you think that you or a child in your care may have signs of autism, it is recommended that you speak to a medical professional.

Q: Where can I find more information about autism?
A: More information, e.g. on the causes and management, or treatment of autism, can be found in our general autism resource.


  1. National Institute of Child Health and Human Development. “About Autism.” January 2017. Accessed June 12, 2018.

  2. Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition.

  3. Centers for Disease Control and Prevention. “Signs & Symptoms.” April 2018. Accessed September 13, 2018.

  4. Autism Speaks. “DSM-5 Diagnostic Criteria.” Accessed September 13, 2018.

  5. MSD Manuals: Professional Version. “Autism Spectrum Disorders.” April 2018. Accessed September 13, 2018.

  6. National Human Genome Research Institute. “Learning About Autism.” January 2017. Accessed September 13, 2018.

  7. Autism Speaks. “Researchers develop first autism symptom self-assessment for adults.” August 12, 2015. Accessed December 18, 2018.

  8. Archives of Psychiatric Nursing. “Exploring the Experience of Self-Diagnosis of Autism Spectrum Disorder in Adults.” October, 2016. Accessed December 18, 2018.

  9. Anatolian Journal of Psychiatry. “Genetic testing in children with autism spectrum disorders.” 2015. Accessed December 20, 2018.

  10. UpToDate. “Autism spectrum disorder: Evaluation and diagnosis.” October 23, 2018. Accessed January 22, 2019.

  11. Mencap. “Autism and Asperger's syndrome.” Accessed September 13, 2018.

  12. American Academy of Pediatrics. “AAP urges continued autism screening in addition to more research.” February 2016. Accessed September 13, 2018.

  13. National Institute of Neurological Disorders and Stroke. “Autism Spectrum Disorder Fact Sheet.” September 2015. Accessed September 13, 2018.

  14. National Institute of Mental Health. “Autism Spectrum Disorder.” March, 2018. Accessed December 20, 2018.

  15. Genetics Home Reference. “ADNP Syndrome.” March, 2017. Accessed December 20, 2018.

  16. Agency for Toxic Substances & Disease Registry. “Lead Toxicity.” June, 2017. Accessed December 20, 2018.

  17. WebMD. “Can Adults Get Diagnosed on the Autism Spectrum?” Accessed September 13, 2018.

  18. Journal of Autism and Developmental Disorders. “Assessing Autism in Adults: An Evaluation of the Developmental, Dimensional and Diagnostic Interview-Adult Version.” February 2018. Accessed September 13, 2018.

  19. Centers for Disease Control and Prevention. “Related Topics.” April 2018. Accessed September 13, 2018.

  20. Pediatrics. “Factors Associated With Age of Diagnosis Among Children With Autism Spectrum Disorders.” December, 2005. Accessed December 19, 2018.

  21. Autism & Developmental Language Impairments. “Predictors of the age of autism spectrum disorder diagnosis: A North Carolina Cohort.” January 10, 2018. Accessed December 19, 2018.