How Autism Is Diagnosed

There are no lab or imaging tests able to diagnose autism. The process involves a battery of evaluations, observations, and interviews to determine whether a person meets the diagnostic criteria of autism spectrum disorder (ASD) as outlined in the American Psychiatric Association's Diagnostic and Statistical Manual for Mental Disorders (DSM-5).

This article walks you through what it takes to diagnose ASD, including the exclusion of other conditions with similar features to autism.

Child lining up toys
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Signs and Symptoms of Autism

If you think that you or a loved one has autism, you will probably have noticed certain signs and symptoms that are characteristic of this developmental disorder. The signs can vary by age as well as the type of autism a person has (such as high-functioning versus low-functioning autism).

The signs are broadly categorized as either being social (how the person interacts and communicates both verbally and non-verbally) or behavioral (how the person behaves in relation to the expected norm).

The signs of autism are usually recognized by parents when a child is between the ages of eight and 10 months. For individuals with high-functioning autism, the signs may not be recognized until they are well into their adult years.

Social characteristics of autism commonly recognized in children include:

  • Avoiding or being unable to maintain eye contact
  • Not responding to their name by nine months
  • Not showing facial expression by nine months
  • Not playing games like pat-a-cake by 12 months
  • Using few, if any, gestures like waving goodbye by 12 months
  • Not sharing expressions of interest (like showing you an object they found) by 15 months
  • Not pointing to objects or people by 18 months
  • Not noticing when others are hurt or upset by 24 months
  • Not noticing other children or joining them in play by 36 months
  • Not engaging in imaginative play (like pretending to be a superhero) by 48 months
  • Not singing, dancing, or play-acting by 60 months

Behavioral characteristics commonly recognized in children with autism include:

  • Playing with toys the same way every time
  • Focusing on specific parts of an object (like a wheel on a toy car)
  • Getting upset when the order of things is changed
  • Flapping hands, rocking the body, or spinning in circles (called stimming)
  • Repeating words or phrases over and over (called echolalia)
  • Following certain routines ritualistically
  • Having abnormal sensitivity to sounds, smells, tastes, appearances, or textures (called sensory hyperstimulation)

Common Tests Used to Diagnose Autism

Autism can often be diagnosed at 18 months of age or even younger. By age two, a diagnosis of autism by a qualified healthcare provider can usually be considered reliable.

The diagnosis may involve watching the child in a structured environment, asking the parents or caregivers a battery of questions, or providing them with a series of questionnaires.

There are four tests commonly used by mental health professionals to help diagnose autism in toddlers and young children:

Autism Diagnostic Interview-Revised (ADI-R)

The Autism Diagnostic Interview-Revised (ADI-R) is a structured interview conducted with parents or caregivers to help differentiate autism from other possible causes. It is intended for children who are at least two years old.

The interview takes around one to two hours to complete and involves 93 questions that assess the child's current and past behaviors. These include questions related to communication skills, social interactions, play behaviors, and repetitive or restricted behaviors.

The response to each question is rated on a scale of 0 to 9 as follows:

  • 0: Behavior is not present
  • 1: Behavior is noted but not sufficient enough to meet the criteria
  • 2: Definite abnormal behavior
  • 3: Extreme severity of the behavior
  • 7: Definite abnormality but not of the type specified
  • 8: Not applicable
  • 9: Not known or asked

After the score is tallied, an algorithm is applied to establish whether autism is the likely cause of the child's behavioral issues.

The ADI-R is widely accepted as a reliable diagnostic tool for autism when used in conjunction with other evaluative tests.

Social Communication Questionnaire (SCQ)

The Social Communication Questionnaire (SCQ) is a screening companion to the ADI-R. It takes around 10 minutes to complete and asks parents or caregivers questions about the child's behavior over both the past three months and their lifetime.

In total, 40 questions are asked, each requiring a simple "yes" or "no" response. Abnormal behaviors are assigned a score of 1.

A total score of 15 or more suggests a higher probability of autism (although scores of 11 or above may warrant further evaluation).

As with the ADI-R, the SCQ assesses the child's social interactions and communication skills, while establishing if there are any restricted or repetitive behaviors commonly seen with autism.

In some cases, the SCQ is used to determine whether the ADI-R is needed. At other times, the tests are performed at the same time to see if the results concur.

Modified Checklist of Autism in Toddlers (M-CHAT)

The Modified Checklist for Autism in Toddlers, Revised (M-CHAT-R) is designed specifically for children between 16 and 30 months of age. It is often the first test given to determine whether further evaluation is needed.

For the M-CHAT-R, parents or caregivers are asked 20 questions about their child's behavior, including:

  • Whether the child pretends or engages in pretend play
  • Whether the child points to something when prompted
  • Whether the child follows a point by someone else
  • Whether the child engages in protodeclarative pointing (pointing to share interest or attention about an object)

The test takes around 20 minutes to complete. Based on the responses, the M-CHAR-R can determine if a child is at "low," "medium," or "high" risk of autism.

Screening Tool for Autism in Toddlers & Young Children (STAT)

The Screening Tool for Autism in Toddlers & Young Children (STAT) is an interactive test used to screen for autism in children between 24 and 36 months of age.

The STAT is a play-based test consisting of 12 different activities. It evaluates how a child interacts and communicates, including their ability to imitate or request and direct attention. A ball, truck, doll, bubbles, and balloons are among the tools used for the test.

The evaluator rates each activity as either "pass," fail," or "refused." The total score ranges from 0 (indicating a low risk of autism) to 4 (indicating a high risk of autism). A score of 2 or above warrants further evaluation.

Differential Diagnoses

Autism is difficult to diagnose because there are many other conditions with similar symptoms. Some are developmental, while others may be neurological (related to the brain and nervous system) psychiatric (related to a mental illness), or pathological (related to a disease).

To ensure a reliable diagnosis, all other possible causes must be excluded, some of which may include:

These are only some of the conditions that may be explored in the differential diagnosis. As a result, it can often take time to reach a definitive diagnosis, particularly if the results of the autism tests are borderline.

Summary

There are no lab or imaging tests able to diagnose autism spectrum disorder (ASD). Instead, autism is diagnosed based on a battery of tests that evaluate a child's behaviors, social interactions, and communication skills. The test may involve interviews or questionnaires with parents or caregivers and/or play-based activities with toddlers and children suspected of having autism.

Tests commonly used include the Autism Diagnostic Interview-Revised (ADI-R), the Social Communication Questionnaire (SCQ), the Modified Checklist for Autism in Toddlers, Revised (M-CHAT-R), and the Screening Tool for Autism in Toddlers & Young Children (STAT).

A parent's recognition of the signs and symptoms of autism is key to an early diagnosis.

A Word From Verywell

The tests used for the diagnosis of autism are only as good as the professional administering them. As straightforward as the tests may seem, they require extensive training to not only administer them correctly but interpret them accurately. The tests are not meant to be self-administered.

Among the healthcare providers qualified to administer the ADI-R and other autism tests are clinical psychologists, developmental pediatricians, and pediatric neurologists. Adults suspected of having autism will usually see a psychologist or psychiatrist.

Whichever healthcare provider you choose, make sure that they are trained and qualified in the diagnosis and treatment of autism. Do not hesitate to ask for credentials or references.

Frequently Asked Questions

  • At what age should a child be tested for autism?

    Children can be tested for autism as early as 18 months or even younger. Most can be reliably diagnosed by age two if evaluated by a qualified mental health professional like a pediatric neurologist or clinical psychologist.

  • Can autism go undetected?

    Autism is frequently diagnosed in children but often undetected for years in adults. This may be because they have high-functioning autism or have simply learned to compensate for their disabilities over time. Despite being able to cope, people with undiagnosed autism are at greater risk of depression, anxiety, and isolation.

  • How is autism diagnosed in adults?

    There is currently no standard procedure for diagnosing autism in adults. A diagnosis will ultimately rely on an evaluation of your behavioral history by a neuropsychologist, psychiatrist, or other mental health professional. Autism-specific questionnaires may be used in tandem with medical tests to exclude all other possible causes.

9 Sources
Verywell Health 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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By Lisa Jo Rudy
Lisa Jo Rudy, MDiv, is a writer, advocate, author, and consultant specializing in the field of autism.