How Is Autism Spectrum Disorder Classified? DSM-5 Criteria and Severity Levels

In this chapter, we'll explain in plain language the official framework your doctor and therapists use to make a diagnosis of autism and to describe its severity, the criteria of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). The World Health Organization's ICD-11 classification system also uses a largely similar framework; there is no important practical difference between the two systems.

DSM-5 Diagnostic Criteria: Two Main Areas

According to DSM-5, for a diagnosis of autism, signs need to be present in the following two main areas, and these signs need to have appeared in the early developmental period and to noticeably affect daily functioning:

• A) Persistent difficulties in social communication and social interaction — this covers difficulties in reciprocal social-emotional interaction, in nonverbal communicative behaviors (eye contact, facial expressions, gestures), and in developing and maintaining relationships. For a diagnosis, signs are looked for in all three of these subareas.
• B) Restricted, repetitive patterns of behavior, interests, or activities — at least two of four subitems need to be present: stereotyped/repetitive movements or speech, insistence on sameness/adherence to routines, very narrow and intense interests, and over- or under-responsiveness to sensory input.

The signs in these two areas will each be covered separately, with concrete examples, in Part Two of the book (Chapters 6–9). DSM-5 also states that the signs need to have been present in the early developmental period, but may only fully emerge when social demands exceed capacity (for example, starting school or entering a crowded setting); this explains why some children go "unnoticed" until age 3–4.

Severity Levels: "How Much Support Is Needed?"

DSM-5 defines autism not as a single category, but with three severity levels determined separately for each of the two main areas. These levels don't show "how autistic" a child is, but rather how much support they need in daily life, and they can change over time, especially with the right support.

Level 1 — Requiring Support

Although noticeable difficulties in social communication may be apparent, with support the child can initiate social interaction and maintain some relationships. They may have trouble adapting to changes in routine, and difficulties may be seen in organization and planning skills, but this difficulty doesn't severely limit daily functioning. Example: a school-age child can communicate with classmates but may have trouble keeping up a back-and-forth conversation, changing the subject, or understanding subtle jokes or hints; they may prefer to be alone at recess.

Level 2 — Requiring Substantial Support

There are noticeable deficits in verbal and nonverbal social communication skills; initiating social interaction without support is rare. Repetitive behaviors and/or insistence on sameness are easily noticed even by a casual observer and affect functioning across a range of settings. Example: a child may communicate with a limited number of words, and a small change in their daily routine (a different route, a different plate) may lead to intense distress.

Level 3 — Requiring Very Substantial Support

Severe deficits in verbal and nonverbal social communication skills lead to very marked impairments in daily functioning; initiating social interaction is extremely limited. Adapting to changes in routine is extremely difficult, and repetitive behaviors clearly interfere with all areas of daily life. Example: a child may communicate with very little verbal language or may not speak at all, may react to changes in routine to a degree that can threaten their safety, and may need intensive support in nearly all daily activities.

Caution / When to Seek Advice

A severity level should be thought of not as a "label" but as a summary of the current need for support. A child's level can change as they develop; the same child can show a different level of support need in different settings (for example, at home versus in a crowded classroom). The words "Level 2" written in a report are not a permanent judgment about your child's future.

Additional Specifiers

In addition to the severity levels, DSM-5 suggests that the doctor add the following specifiers to the diagnosis:

• Whether there is an accompanying intellectual disability
• Whether there is an accompanying language disorder (and if so, what level the functional language is at)
• Whether it is associated with a known medical/genetic condition or environmental factor
• Whether there is another accompanying neurodevelopmental, mental, or behavioral condition (such as ADHD, anxiety, or epilepsy)
• Whether it is associated with catatonia

This additional information helps personalize the treatment plan by creating a full clinical picture. For example, a diagnosis worded as "autism spectrum disorder, Level 2, with accompanying language disorder, associated with a known genetic condition (Fragile X syndrome)" carries far more clinical information than simply saying "autism" and guides the treatment team.

Differential Diagnosis: Conditions That Can Be Confused with Autism

Some developmental and behavioral conditions can bear surface similarities to autism and need to be carefully told apart by an experienced clinician: social (pragmatic) communication disorder (social communication difficulty alone, without repetitive behaviors), hearing loss (which can lead to social withdrawal and language delay), severe language disorder, attention deficit hyperactivity disorder, severe early childhood anxiety, and, rarely, some genetic syndromes that involve very early-onset developmental disorders. This differential diagnosis process will be covered in detail in Part Three of the book.

Info Box

A diagnosis requires signs in two main areas (social communication; repetitive behavior/narrow interests).

The severity level (1, 2, or 3) is determined separately for each area and can change over time.

The additional specifiers added to the diagnosis (accompanying intellectual disability, language disorder, known genetic condition, etc.) create a full clinical picture.

Conditions that resemble autism but require a different approach must be told apart.

This classification system forms the basis of the diagnosis process (history, observation, standard scales) that will be covered in the next part.

Chapter Summary — Closing Part One

In this first part, we looked at how the brain develops, the neurobiological basis of autism, common false beliefs, current prevalence data, genetic and environmental causes, and the official diagnostic classification. This foundational knowledge lays the groundwork you'll need to understand, in Part Two, in much more concrete and detailed terms, how autism looks in daily life, from social communication difficulties to sensory sensitivities, from early signs to accompanying conditions.