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Autism – The Path to Diagnosis

Written by Kelly Crumrin
Posted on August 11, 2018

The path to a diagnosis of autism usually begins with a pattern of “red flags” such as missed milestones, developmental delays, communication difficulties, and unusual behaviors. Parents, teachers, or the child’s doctor may notice initial symptoms. Recognizing and diagnosing autism as early as possible is vital, since early intervention and treatment significantly improve outcomes for children with ASD.

While some children may show signs of autism within the first few months of life, the average age of diagnosis in the United States is between ages 3 and 6. Some researchers believe that a conclusive diagnosis can be made by age 2, although others believe it is possible to reliably diagnose ASD at 18 months. Older children and adolescents may be recommended for evaluation and diagnosis by teachers. Diagnosing autism in adults is more complex.

How Is Autism Diagnosed?

Autism spectrum disorder (ASD) cannot be diagnosed with a medical exam such as a blood test.

The fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) lays out diagnostic criteria for autism spectrum disorder in two areas:

  • Persistent deficits in social communication and social interaction across multiple contexts
  • Restricted, repetitive patterns of behavior, interests, or activities

The DSM-5 cites specific examples and describes the context in which problems should be viewed as potential evidence as autistic traits. The DSM-5 goes on to provide criteria for rating the severity levels of problems in both areas. Severity levels are:

  • Level 1 – Requiring support
  • Level 2 – Requiring substantial support
  • Level 3 – Requiring very substantial support

Screenings and school evaluations may catch symptoms of ASD, but they cannot provide a diagnosis. Only a doctor or specialist can diagnose autism.


Screening is often the first step toward diagnosis for children with ASD. Children are increasingly screened for symptoms of autism at 18-month and 24-month well-child visits to the pediatrician or family physician. Screenings do not provide a diagnosis but are designed to detect early symptoms. Initial screening involves a questionnaire about developmental milestones that is completed by the parent. If milestones are delayed or if the parent has concerns, the child may be referred to a specialist for more in-depth assessment.

School Evaluations

For school-age children with disabilities, a school evaluation or educational determination may be requested by the parent or recommended by the school as the first step in obtaining special education services and an individualized education program (IEP). The evaluation is made by a team of education professionals and focuses on rating the level of disability and determining what services will be needed. The evaluation does not provide a diagnosis. An independent evaluation can be obtained if the parents disagree with the results of the school evaluation.

Diagnosis of Autism

Typically, autism is diagnosed by a doctor such as a developmental pediatrician, child psychologist, child psychiatrist, or neuropsychologist. Speech and language pathologists may also be involved in autism diagnosis. It is important to choose a specialist experienced in diagnosing ASD.

There is no single test to diagnose autism. Instead, the doctor will begin by taking a thorough medical, family, and developmental history. Since risk factors for autism include both genetic and environmental factors, an autism assessment may include questions about:

  • Family history of genetic disorders, epilepsy, or developmental problems
  • The mother’s health during pregnancy
  • Exposure to toxins during pregnancy or infancy

A clear picture may emerge from the medical history to help the doctor assess risk factors that strengthen the suspicion of autism or rule out other conditions. The doctor will perform a physical exam of the child and will likely ask questions about:

  • Seizures
  • Allergies
  • Gastrointestinal problems such as frequent constipation or diarrhea
  • Sleep habits
  • Developmental milestones
  • Behavior patterns
  • Sensory challenges

Neuropsychological Testing

The doctor will likely perform or order a neuropsychological assessment. A “neuropsych eval” may consist of one appointment lasting between four and eight hours or be spread over multiple appointments. During the evaluation, the neuropsychologist will observe the child’s behavior and provide the child with tasks that allow them to assess cognitive functioning, verbal and nonverbal reasoning, usage of language and communication, and motor skills.

Apart from furnishing a diagnosis, the results of a neuropsychological assessment can help parents and schools better understand how the child learns and how best to meet their educational needs.

Other Tests

Blood or saliva tests may be ordered to check for genetic syndromes such as Rett, fragile X, Prader-Willi, or Angelman that are often associated with autism.

The doctor may order screening tests to determine whether the child has any problems with hearing or vision. Hearing and vision impairments are sometimes mistaken for autism, and in cases where a child has both autism and sensory impairments, it can complicate the diagnosis.

What Is the Prognosis for Autism?

ASD is a lifelong condition for nearly all people. Fortunately, autism treatments have been shown effective at improving outcomes, especially when therapy begins early.

Approximately one-third of people with autism never begin talking, although many learn nonverbal forms of communication. Approximately one-third of autistic people have intellectual disabilities, while the rest have average or significantly above-average intellectual abilities.

A 2015 study of 1,420 children originally diagnosed with autism found that 3 percent had “optimal outcomes,” meaning that they eventually lost all symptoms of autism. Most of these individuals were high-functioning to begin with, showing mild behavioral symptoms. More research on the permanence of autism is needed.

What Are the Early Signs of Autism?

Every child develops differently, and developmental milestones are attained at different ages. However, the earlier autism is recognized and treated, the better the outcome for the child.

Warning signs of autism within the first year of life can include no social smiling, babbling, or watching faces by 3 months; no sitting, reaching, enjoyment of social play, or responding to their name at 7 months; and not saying “mama” or “dada,” using simple gestures, or eating with hands by around 12 months. Read more about symptoms of autism at different ages.

How Is Autism Diagnosed in Adults?

No one knows how many adults are living with autism. Before testing became standardized and screening became prevalent, many people grew up without their autism ever being diagnosed or treated. Some adults seek diagnosis themselves after one of their children receives a diagnosis of ASD.

Current diagnostic protocols are designed for assessing children, not adults. However, adult-focused autism assessment tools are under development. Diagnosis in adults is more complicated since most autistic adults have developed strategies over the years to compensate for challenges and disabilities. The process of assessing an adult for autism spectrum disorder will involve in-depth conversations with a clinician about the adult’s early childhood and developmental history, as well as current challenges around communication, social interaction, repetitive behaviors, and sensory issues. If possible, it may help for the clinician to discuss the adult’s early developmental history with an older relative who may remember more details.

It may be difficult to find a specialist familiar with diagnosing autism in adults. If you have a child with autism, the specialist who diagnosed them may be able to help you or recommend another professional who can. Some psychologists or psychiatrists may be qualified. Conversely, some developmental pediatricians, pediatric neurologists, or child psychologists may be willing to assess autism in an adult.

Condition Guide


External resources

MyAutismTeam resources


Are there other conditions that can be confused with autism?
Differential diagnosis is the process of distinguishing one condition from other conditions that present with similar signs and symptoms. Depending on the age of the person being assessed for autism, the differential diagnosis must take into consideration several different neurological and psychological disorders, genetic conditions, and developmental and behavioral problems. Since it is common to have autism along with other conditions, diagnosis can be complicated.

Below are a few of the most common conditions that can both accompany and confuse the process of diagnosing autism spectrum disorder.

Sensory processing disorder (SPD)
Previously known as sensory integration dysfunction (SID), SPD makes it difficult for people to correctly receive and interpret sensory information and act upon it appropriately. People with SPD may over- or under-respond to sensory stimuli. Research indicates that as many as 75 percent of autistic children also have SPD.

Attention-deficit/hyperactivity disorder (ADHD)
Researchers estimate that half of children with autism also have ADHD. Autism and ADHD seem to involve changes to the same genes. People with ADHD may show signs of inattention, hyperactivity, or both.

Social (pragmatic) communication disorder (SCD)
SCD describes difficulties in social interaction, verbal and nonverbal communication, understanding of social situations, and pragmatics (language as used within different contexts). There is significant overlap between symptoms and behaviors in SCD and autism spectrum disorder. In fact, ASD must be ruled out before SCD can be diagnosed.

Obsessive-compulsive disorder (OCD)
According to one study, 17 percent of children with autism also have symptoms of OCD. Unlike repetitive behaviors common in autism alone, OCD behaviors contain an element of obsessive belief that performing the rituals will prevent something bad from happening.

Anxiety disorders
Problems with anxiety, including phobias and panic disorders, are common among people with autism.

Intellectual disability
Approximately one-third of autistic people have intellectual disabilities, while others have average or significantly above-average intellectual abilities.

Untreated phenylketonuria (PKU)
Left untreated, people with the genetic disorder PKU gradually develop a wide variety of physical, cognitive, and behavioral problems as they consume protein-rich foods or products containing the artificial sweetener aspartame. Untreated PKU can cause intellectual disabilities, seizures, hyperactivity, and delayed development among other issues.

Genetic syndromes
Several genetic syndromes can cause symptoms similar to those seen in autism spectrum disorder. There is often significant overlap between some genetic syndromes and autism, which can complicate diagnosis or result in a dual diagnosis.

  • Rett syndrome is almost exclusive to girls and involves severe motor disabilities.
  • Fragile X affects boys more often and more severely. It may involve specific physical features as well as some degree of intellectual disability.
  • Prader-Willi causes delayed development, learning disabilities, and an insatiable appetite that often leads to obesity.

Angelman syndrome causes intellectual disabilities, movement and balance problems, and abnormal sleep patterns.

Posted on August 11, 2018
All updates must be accompanied by text or a picture.

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Kelly Crumrin is a senior editor at MyHealthTeam and leads the creation of content that educates and empowers people with chronic illnesses. Learn more about her here.

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