Diagnosing ASD

Diagnosing Autism Spectrum Disorder

The most recent version of the Diagnostic & Statistical Manual (DSM; a diagnostic tool for mental health practitioners) diagnostic criteria, DSM-5, combined autism, Asperger’s syndrome and pervasive developmental disorder into a single diagnosis and changed the name of this group from “Pervasive Developmental Disorders” to “Autism Spectrum Disorder” (APA, 2013).

Although the category remains broad, DSM-5 no longer provides differing criteria for each condition, instead a single set of criteria with several specifiers allowing the diagnostician to indicate the presence of certain features and to rate severity.

The current DSM-5 diagnostic criteria is presented below, along with examples of the characteristics.

Based on the DSM-5, autism can be behaviourally defined by diagnostic criteria specifying pervasive qualitative differences in social and communication skills and behaviour. However, as yet, there are no definitive medical tests, biochemical, neuroimaging or otherwise to detect autism. Hence, diagnosis relies heavily on detailed history and observation of behaviour by skilled clinicians using the DSM-5 and/or ICD-10 (another diagnostic tool for mental health practitioners) criteria.

There are International Assessment Guidelines, such as NICE (National Institute for Health and Care Excellence). The guidelines indicated that an autism assessment can include:

  1. Screening – based on client and informant.
  2. Clinical History – based on DSM or ICD diagnostic criteria.
  3. Observational assessment – clinical and ADOS-2.
  4. History of functioning outside the clinical setting.
  5. Developmental History: both clinical history and ADI-R.
  6. Individual profiling e.g., intellectual abilities, communication skills, adaptive skills, sensory profile where relevant.
  7. Assessment for co-occurring physical (e.g., gastrointestinal), neurological disorders (e.g., epilepsy), and/or mental illness (e.g., mood or anxiety disorders).
  8. Assessment of risks (e.g., self-harm, escalation of problems, harm of others).
  9. No use of biological tests, genetic tests or neuroimaging (e.g., MRI, EEG) for diagnostic purposes.

Note: A recent systematic review by Wigham et al (2018) advises caution when using screening questionnaires with patients with a co-occurring mental illness; interpretation is less reliable as screening tools are less sensitive and specific discrimination between ASD and a mental illness is required.