What Are Diagnostic Criteria?

How are disorders such as autism diagnosed?

Before we talk about the proposed changes to the DSM criteria for autism, let’s go right back to the beginning and talk about what diagnostic criteria are and why we need them.

What are diagnostic criteria?

Autism is a disorder that’s identified solely by behaviour – there’s no blood test, DNA screening or secret tattoo that tells you whether someone is autistic. So in order for a diagnosis of autism to have any meaning, everyone needs to agree on just what those behaviours are. It would be impossible to provide support, distribute funding or conduct research if we didn’t have a consistent understanding of what autism looks like.

The different sets of diagnostic criteria were developed to provide this common language for identifying and describing autism. Put simply, they’re a checklist of the behaviours that must be present before someone can officially be considered autistic.

How are the criteria used?

Information about the way a person thinks, reacts and behaves is collected and compared against each one of these standards (criteria). A judgement is then made as to whether the criterion has been met – does the behaviour match the description?

This is the tricky part, because there’s no cut-off score or yes-no answer that can definitively decide whether a criterion has been met. A judgement call has to be made using the weight of the evidence that has been collected, and this leaves a lot riding on individual interpretation of the wording and intent of the criterion – not to mention the extent of the diagnostician’s experience with autism and the thoroughness of their data gathering.

It’s just one of the reasons why diagnosing autism can sometimes be a complicated process.

The Autism Spectrum Disorders (ASDs)

Note: this section has been updated to reflect the changes in DSM-5 that came into effect after this article was first published.

Before DSM-5, the diagnostic criteria also served another purpose – to distinguish between the individual disorders which make up the autism spectrum:

  • Autism or Autistic Disorder
  • Aspergers or Asperger Syndrome
  • Pervasive Developmental Disorder – Not Otherwise Specified

The criteria for Aspergers were slightly different to those for Autism, making it theoretically possible to diagnose these as separate disorders. This was highly contentious however, with many people believing that there is no clear evidence to suggest that Aspergers exists as a separate disorder.

The handling of Aspergers as a separate entity is one of the biggest areas of change in DSM-5, so we’ll be looking at that in more detail later.

PDD-NOS on the other hand didn’t have any criteria of its own – it was diagnosed solely by exclusion using the criteria for the other two. If someone had autistic behaviours but not enough to meet the criteria for a diagnosis of either Autism or Aspergers (or the criteria that are met are not in the correct combinations for those diagnoses) then a diagnosis of PDD-NOS may have been given.

PDD-NOS was also sometimes the diagnosis given when autistic behaviours first appeared after the age of three.

What the criteria can’t tell us

Contrary to popular belief, it’s not the case that the more criteria that are met then the more severe the autism. The current criteria don’t give any indication of severity or prognosis (e.g. high or low functioning, mild or moderately impaired). Impairment and functioning levels are decided in the context of the complete set of evidence – for example, whether there’s an intellectual and/or language delay and the degree to which daily living skills are affected.

It’s also common to see PDD-NOS referred to a kind of Autism Lite, but this simply isn’t true. A child diagnosed with PDD-NOS can meet the same number (or more) of the criteria as someone given an Autism diagnosis, just not in the combination required to be officially classified as autistic.

It’s also important to remember that the criteria are an attempt to apply a universal definition to a complex disorder that varies greatly amongst individual people. As such, they can’t (and don’t) adequately describe all the many aspects of what it means to be autistic. The terminology is centred on deficit and impairment, which takes a very narrow view of what being autistic is like. And as autism is classified as a developmental disorder, the focus is very much on children.

So now that we know what diagnostic criteria, why we need them and some of their limitations, let’s move on to looking at the specific sets used to diagnose autism.

Last updated 23 Nov, 2017 by Bec Oakley

Bec Oakley is an autistic writer and proud parent, with an intense passion for 80s text adventures, Twizzlers and making the world a better place for autistic people and their families.