How Autism Is Diagnosed

Six year old boy working with a psychologist at the psychotherapy session.

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There is no physical test to diagnose autism spectrum disorder (ASD) which can often make diagnosing the condition difficult. For a diagnosis of ASD to be made, a doctor will take a look at a person’s medical and developmental history.

ASD can be detected in children as young as 18 months old and, in some cases, even younger. However, it might take a little more time to make a definite diagnosis. In many autistic children, the condition might go undetected until they are teenagers or adults.

At-Home Testing 

It’s inadvisable to make a final diagnosis of ASD at home, but there are some early signs you could look out for, especially in children. An autistic child might have difficulty maintaining eye contact with people. Their communications skills might also be behind that of children the same age.

While children who don’t have the disorder might have started communicating with more than a couple of words by the age of 18 months, an 18-month-old autistic child might not have yet said their first words. 

You might also notice autistic children get unusually bothered when there’s a slight disruption in the daily routine you’ve created for them. They might throw a tantrum or become completely unresponsive to any form of communication. 

The Center for Disease Control and Prevention has a program called “Learn the signs, act early.” This program helps to provide a guide for families to recognize early signs of developmental concerns like ASD.

It’s important to note that this guide doesn’t serve as a substitute for getting a definite diagnosis from a licensed medical expert or professional. A diagnosis of ASD needs to be made as soon as possible so that autistic children can get the help they need. 

Tests and Scales

While there are no physical tests to help diagnose ASD, several developmental tests and scales can be used to diagnose the condition. The DSM-5 is the standard guide healthcare professionals use to diagnose behavioral and mental conditions. It also provides criteria for ASD.

However, other tests have been developed to fill in the gaps for an autistic person who doesn’t fit into the DSM-5's highlighted criteria. 

Developmental Screening 

According to the American Academy of Pediatrics (AAP), all children should be screened for ASD during their regular doctor visits at 18 months and two years old. If a child is considered at a higher risk of developing ASD, a doctor might conduct these screenings more regularly.

Children whose parents or siblings have a history of the condition are at a higher risk of developing the condition. A developmental screening will typically involve a series of questionnaires about your child’s development by a medical professional or expert. If the screening identifies signs and symptoms that hint at ASD, further evaluation might be needed to make a definite diagnosis.

Further evaluation will include speaking to a doctor specializing in child development or a child psychologist who specializes in brain development. ASD also often co-occurs with other conditions; a healthcare professional might also order a blood test and a hearing test.

Diagnostic Interview for Social and Communication Disorders (DISCO)

DISCO is an interview-style test used to enquire about a person’s developmental behaviors through their day-to-day functioning. Medical experts can use the DISCO to diagnose ASD in both children and adults.

The DISCO is a helpful diagnostic tool for individuals who can’t provide a detailed history of developmental behaviors categorized under ASD. Tests like screening with the DSM-5 typically need a developmental history before a diagnosis can be made. However, the DISCO should be used alongside standardized assessments as with that in the DSM-5.

Autism Diagnostic Interview-Revised (ADI-R)

The ADI-R has also been used in diagnosing ASD in adults and children. Its focus is on the quality of communication, social interaction, and restricted and repetitive behaviors when trying to make a diagnosis.

Autism Diagnostic Observation Schedule (ADOS) 

ADOS is a tool used to assess social interactions and communications in people with ASD or might be at risk of developing the condition. The ADOS can be used to diagnose the condition in both children and adults. It’s also a great tool for people at any stage of ASD. People with severe ASD who might not communicate verbally at all will benefit from the ADOS assessment systems.

Diagnosing Autism

Certain other conditions that used to be diagnosed separately are now classified under ASD. Conditions like Asperger’s syndrome and pervasive developmental disorder not otherwise specified (PDD-NOS) are now considered ASD. The American Psychiatric Association’s Diagnostic and Statistical Manual, Fifth Edition (DSM-5), provides certain standard criteria that are typically used to diagnose ASD.

According to the DSM-5, for a child to be diagnosed with ASD, they should have persistent problems in the following areas of social communication and interaction. 

  • Having persistent and abnormal social interactions 
  • Difficulty in understanding non-verbal communication or communicating with non-verbal cues 
  • Difficulty maintaining and developing relationships with people 

The DSM-5 also requires the child to exhibit at least two of the following restricted, and repetitive types of behaviors autistic people typically have: 

  • Being overly sensitive or under-sensitive to sensory stimuli like sounds, smells, or tastes 
  • Sticking to rigorous routines and becoming upset at the slightest disruption of their routines 
  • Becoming fixated with particular interests at an abnormal intensity 
  • Engaging in repetitive movements or speech 

These symptoms are typically required to have been present at an early age and significantly impair their daily functioning. Intellectual development disorder will also need to be ruled out for a conclusive diagnosis to be made. 

During an assessment, the parent or guardian of the child suspected to be living with the condition will be asked about their child’s development history. They’ll also be asked about how their child plays and interacts with other people. 

For adults, during an assessment, you’ll be asked to fill a questionnaire about developmental problems you might have experienced over the years. If available, they might also ask to speak to someone who knew them as a child, as it’s most likely that the condition developed in childhood and persisted into adulthood.

How It All Fits Together 

Diagnosing ASD can be very difficult, mainly because the condition starts to manifest itself early. The families of people living with the condition have to watch for early signs and symptoms in their children from as early as 18 months old.

They should also do a developmental screening test with a certified healthcare professional who will put their child through a series of questionnaires and checklists. An ASD diagnosis helps the families of autistic people understand their needs and how best they can support them.

For an adult who has lived for years with the condition, a diagnosis of ASD could finally answer any questions they’ve had for most of their lives. They’ll understand why they find doing certain things harder than most people or find it challenging to communicate with people or be comfortable in social settings.

9 Sources
Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Centers for Disease Control and Prevention. What is a developmental milestone? January 22, 2021

  3. National Institute of Mental Health. Autism Spectrum Disorder. March 2018

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  5. Lord C, Rutter M, Le Couteur A. Autism Diagnostic Interview-Revised: A revised version of a diagnostic interview for caregivers of individuals with possible pervasive developmental disorders. J Autism Dev Disord. 1994;24(5):659-685. doi:10.1007/bf02172145

  6. Hus V, Lord C. The autism diagnostic observation schedule, module 4: revised algorithm and standardized severity scores. J Autism Dev Disord. 2014;44(8):1996-2012. doi:10.1007/s10803-014-2080-3

  7. University of Washington. DSM-5 Autism Spectrum Disorder. February 2013

  8. NHS UK. What happens during an autism assessment. April 18, 2019

  9. NHS UK. Autism: How to get diagnosed. April 18, 2019

By Toketemu Ohwovoriole
Toketemu has been multimedia storyteller for the last four years. Her expertise focuses primarily on mental wellness and women’s health topics.