Diagnostic Assessments for Autism

What is autism?

Autism is a lifelong developmental condition that affects how people understand and interact with the world. It is called a spectrum condition because autistic individuals present in many different ways. For example, some people may have a co-occurring learning disability or high support needs, while others may not require additional support.

Autistic people, like everyone, have different strengths and needs. However, all autistic people share common areas of difference, which may affect them in different ways:

Social interaction and communication

Routines, repetitive behaviours, and intense interests

Many autistic people also experience mental health difficulties. There are many strengths associated with being autistic, such as having expertise in a chosen topic, being loyal, and having a strong sense of justice.

Diagnostic assessments

Autism assessments must be carried out by professionals with specialist training. A full assessment usually includes:

A detailed developmental history

Observations

Information from someone who knows the person well (e.g. a parent)

Many people are diagnosed in childhood but increasing numbers of adults are seeking assessments due to greater awareness of autism

Diagnostic Criteria

To receive an autism diagnosis, a person must have:

Significant difficulties in:

Social interaction and communication

Restricted and repetitive behaviours, interests, or activities

These difficulties must:

Be lifelong (starting in childhood)
Affect multiple areas of life

There are some examples of diffficulties in the table below. You do not need to experience all possible difficulties, but you must have differences in both areas.

Social interaction and social communication:	Restricted and repetitive behaviours, interests or activities
Differences in making and/or maintaining relationships	Highly focused, all-encompassing interests that may interfere with other aspects of life
Difficulties in understanding and managing emotions	Excessive adherence to routines to an unusual degree
Not easily understanding how other people think or feel	Inflexible thinking (black and white thinking)
Difficulties understanding social rules, or a different view of social rules	Difficulties coping and often extreme distress with change
Differences in speech	Repetitive behaviour or rituals
Repetitive speech	Strong adherence to rules
Difficulties with eye contact	Repetitive or stereotyped movements
Reduced facial expression or gesturing	Over or under-sensitivity to sensory aspects of the environment
Differences in communicating with others	Noticing small details, patterns or sounds that other people do not notice
Difficulties being able to read other people’s non-verbal communication	Intensely focussing on something for a long period of time and struggling to shift focus

The IAS assessment process

The process of diagnostic assessment followed by the IAS adheres to NICE Guidance for ‘Autism: recognition, referral, diagnosis and management of adults on the autism spectrum (NICE, 2012).’

The assessors are all skilled practitioners with a relevant core profession, extensive autism experience, and diagnostic training

The diagnostic team are overseen by the Clinical Lead, a Consultant Clinical Psychologist, the team have regular supervision and ongoing professional development

The team are skilled in assessing autism across different presentations, genders, and masking profiles

What Happens After Referral

Your referral is reviewed by the IAS team.

If sufficient information is provided, you will receive a triage questionnaire.

After returning the questionnaire, you will be offered a triage appointment (usually within 3–6 months).

If a full assessment is indicated:

- You will join the waiting list (currently up to 3 years as of Dec 2025 and likely to increase).

- You will complete two pre-assessment questionnaires (one by you, one by someone who knows you well).

- You will attend a face-to-face assessment (up to 4 hours, longer if complex).

If a full assessment is not indicated, you will be discharged and signposted to other services, if relevant.

Making a Referral

As awareness of autism and neuro-divergence increases, the number of people self-referring for an assessment has also increased. Many people strongly identify as autistic before assessment. However, the outcome may be that you do not meet diagnostic criteria, even if you have traits that overlap with autism. This can feel upsetting or frustrating. Please consider whether you are prepared for this possibility before proceeding.

To refer for an autism assessment please complete this Referral Form

Do the IAS accept private autism assessments?

The IAS supports adults diagnosed with autism. If the diagnosis was made privately or by another service, the IAS will request a copy of the diagnostic report (unless it’s already available on the electronic system, e.g., from child services). Private diagnoses are accepted only if they follow NICE guidance for a full assessment.

When reviewing a private assessment, we check that it meets NICE guidance: Autism – recognition, referral, diagnosis, and management of adults (NICE, 2012). Please ensure your assessment follows these standards.

NICE Requirements for a Full Assessment

Carried out by qualified clinicians

Team-based approach

Includes observational assessment (e.g., direct observation or a tool like ADOS)

Involves a family member, partner, carer, or uses documentary evidence of current/past behaviour and early development

Considers differential or coexisting conditions

Uses formal diagnostic tools for complex cases

Assesses core autism features across life span and includes early developmental history (or explains why not possible)

States whether diagnostic criteria are met according to ICD-11 or DSM-5