Hello, and welcome back to The Autistic Writer. The field of autism is so complex. The difference between a neurodiversity-based approach to autism and a pathologised approach to it is only part of that complexity. But it certainly does generate a lot of confusion.
Today, I want to talk about how to interpret some technical aspects of formal diagnosis of autism. I’m firmly in the camp of the neurodiversity paradigm, but that doesn’t mean I don’t think it’s important to understand formal clinical approaches to autism. Understanding the clinical approach is an important tool to have.
My Story
I’ve told this anecdote several times, probably on this website, but for today’s context, it’s worth mentioning again.
When I received my formal diagnosis of autism, I was labouring under many misconceptions. When the specialist who gave me my diagnosis asked me if I had any questions, I asked her where I was on the spectrum.
Yes, I actually said those words.
She asked me if I was referring to severity, and I confirmed I was indeed asking that question. She then very patiently explained to me that “autism doesn’t really work like that.”
Nevertheless, conversations about severity of autism continue across social media, and the wider media generally. A war of ideas is being waged in autism academia about the issue of alleged severity of autism, with the term profound autism recently entering the chat, and the concept of levels of autism frequently being discussed. I’m going to skip the war of ideas today, and go straight into clearing up some confusion over technical aspects of diagnostics.
Levels and Codes
This whole article was prompted when I came across an online conversation about autism diagnosis. One person suggested that the ICD (International Classification of Diseases) has a coding system for autism that is effectively equivalent to the levels system used by the DSM (Diagnostic and Statistical Manual of Mental Disorders). Another said they had received a diagnosis in the UK that referred to the DSM (an American manual) rather than the ICD (generally used by the rest of the world).
Both claims contain some truth, but they also illustrate how easily confusion emerges when we talk about autism diagnosis.
The Diagnostic and Statistical Manual of Mental Disorders (DSM), published by the American Psychiatric Association, and the International Classification of Diseases (ICD), published by the World Health Organisation, are different classification systems. Their definitions of autism have plenty in common, but the way they organise information about autism diagnosis is different.
Both systems identify two broad areas at the heart of autism:
Area 1: Persistent differences in social communication and social interaction. Area 2: Restricted, repetitive, or inflexible patterns of behaviour, interests or activities.
The DSM 5 explicitly includes hyper- or hyporeactivity to sensory input, or unusual sensory interests, among the possible manifestations of area 2. At least two of four types of restricted or repetitive characteristics must be present for a diagnosis. Sensory differences are just one of those characteristics, so they are not absolutely required for an autism diagnosis, but they can contribute to meeting the DSM diagnostic criteria.
The ICD 11, like the DSM 5, incorporates sensory characteristics into its description of autism, although the two manuals organise and express the diagnostic criteria differently. This represents a change from ICD 10, whose autism criteria did not explicitly include sensory reactivity. UK clinical guidance recommends assessing hyper- and hypo-sensory sensitivities as part of a comprehensive autism assessment.
The DSM then adds something that is particularly familiar from conversations in the autistic spaces online: levels. Level 1 means “requiring support”, Level 2 “requiring substantial support”, and Level 3 “requiring very substantial support”. But these are not three overall grades of autism. The DSM rates severity separately for social communication, and for restricted, repetitive behaviours. The two ratings do not have to be the same.
The ICD 11 has no equivalent Level 1–3 system. Instead, its coding system records whether the person has a co-occurring disorder of intellectual development and the degree of impairment in functional language. For example, an ICD 11 code can distinguish autism without intellectual disability and with mild or no functional-language impairment from autism with intellectual disability and impaired functional language.
This brings us to another potential source of confusion: intellectual disability is not a defining characteristic of autism. An autistic person may have an intellectual disability, average intellectual ability or very high intellectual ability. In the DSM, intellectual disability is therefore specified as something that can accompany autism rather than something that defines it. The ICD 11 similarly records whether a disorder of intellectual development is present.
So an ICD code indicating autism with intellectual disability is not saying that intellectual disability is part of what makes the person autistic. It is describing an additional aspect of their developmental profile. Nor does having an intellectual disability automatically correspond to DSM Level 2 or Level 3. The two systems are measuring different dimensions.
This is also why DSM severity levels should not be interpreted as a simple measure of “how autistic” someone is. A person could have no intellectual disability, and fluent language, but nevertheless require substantial support. Another autistic person could have an intellectual disability, because intellectual ability and DSM autism severity are assessed separately. Intellectual ability, language, autistic characteristics and support requirements are related but distinct aspects of a person’s profile.
So where does the UK fit into all this?
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NHS England’s national framework says ICD 11 should be used for the primary description of autism, but its more recent guidance also says that ICD 10 remains the mandated information standard for national datasets while systems are being updated, while also acknowledging that DSM-based assessment tools and DSM terminology remain in use.
So, there is nothing wrong with a UK diagnostic report referring to DSM 5 criteria. A clinician may use DSM-based assessment tools, or explicitly state that the person meets DSM 5 criteria, even though the NHS’s formal classification system is ICD.
Guidance from NICE (the National Institute for Health and Care Excellence) refers clinicians to both ICD 11 and DSM 5 criteria in the context of autism assessment.
The important thing, then, is not to imagine DSM and ICD as two versions of the same autism “severity scale”. Their descriptions of autism overlap substantially, but they arrange their information differently.
The DSM explicitly incorporates sensory reactivity into its restricted/repetitive area and provides separate severity ratings for social communication and restricted/repetitive behaviours.
The ICD 11 does not use those severity levels and instead incorporates intellectual development and functional language into its autism coding.
Neither system, therefore, gives us a single number that tells us “how autistic” someone is.
It’s useful to remember when encountering autism terminology online that you don’t receive a DSM diagnosis of Level 1, 2 or 3 autism; the DSM uses these levels to describe the support required in two separate areas of autism diagnosis. And it’s equally useful to remember that an autism diagnosis, a DSM severity level, and an ICD code are not describing the same thing.
That’s all for this time. Take care.
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