Autism cannot be diagnosed through a simple blood test or examination. Instead, autism is diagnosed using observation and looking at developmental history. There are two main diagnostic manuals that set out the characteristics of autism.

The International Classification of Diseases version 10 (ICD-10) which is written by the World Health Organisation

The Diagnostic and Statistical Manual of Mental Disorders version 5 (DSM-5), which is written by the American Psychiatric Association.

These diagnostic manuals are updated every few years. When they are being updated, work groups are formed to discuss the latest research and understanding of different conditions and whether this affects the diagnostic criteria.

Our understanding of autism has grown significantly over the past 40 years, and this is reflected in the changes in diagnostic criteria as new versions are released. Up until 2013, the diagnostic criteria for autism were very similar in both manuals. In the UK, both manuals can be used. Best practice guidance for diagnosing children and adults is outlined by the National Institute for Health and Care Excellence (NICE)

Diagnostic manual ICD-10 DSM-5
Version Next version released 2017 Version released May 2013
Diagnostic terms Pervasive Developmental Disorders (PDD) – a category which includes the following separate diagnoses:

  • Childhood autism
  • Atypical autism
  • Rett’s syndrome
  • Asperger syndrome
  • Pervasive developmental disorder, unspecified
Autism Spectrum Disorders: this new umbrella term is a single diagnosis which covers most of the terms listed under ICD-10. Rett’s syndrome is not included as its genetic basis has been identified and it is no longer diagnosed through observation.
Criteria used Three main areas:

  • Communication
  • Social interaction
  • Restricted, repetitive, and stereotyped patterns of behaviour.
Two main areas:

  • Communication and social interaction
  • Restricted, repetitive, and stereotyped patterns of behaviour and sensory issues.

Why did they make the changes in DSM-5?

Probably the biggest change in the DSM-5 was grouping all of the separate diagnoses under one single label – Autism Spectrum Disorder. This decision caused a lot of controversy, especially grouping Asperger syndrome into Autism Spectrum Disorder. The reason for this grouping was that there was no clarity on how each of the separate diagnoses differed from each other, and a number of research studies have shown that the diagnosis you receive depends on the clinician’s preference more than actual characteristics.

There are some drawbacks to having one single diagnosis, especially for research. Because every autistic person is different, classifying them in one big group makes it difficult for researchers to study smaller subgroups. Big categories mean that the groups are more variable which makes the results more difficult to repeat in future research. Researchers are working on defining smaller subgroups for research purposes (for example the Research Domain Criteria (RDoC) created by the National Institute for Mental Health in the US).