# 02 - Making an ICD 11 diagnosis using the CDDR

# Making an ICD-11 diagnosis using the CDDR

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Using the CDDR for ICD-11 mental, behavioural and neurodevelopmental disorders in clinical settings
equivalent phenomenon is experiencing feelings of physical restlessness or a sense of discomfort 
with being quiet or sitting still. Also included in this section are developmental variations that are 
more common in older adults, among whom many mental disorders are often underdiagnosed. 
This section also contains information about different patterns of co-occurring conditions and 
risks for associated sequelae according to developmental stage.
Culture-related features
This section provides information regarding cultural considerations that should be considered 
when making the diagnosis. This includes cultural variations in prevalence and symptoms of 
disorders, sociocultural mechanisms that may account for this variation, and descriptions of 
cultural concepts of distress that are relevant to diagnosis and treatment decisions. See the section 
on cultural factors in the Introduction for additional information.
Sex- and/or gender-related features
This section covers sex- and/or gender-related diagnostic issues, including sex- and/or genderlinked differences in symptom presentation, community prevalence and presentation in 
clinical settings.
Boundaries with other disorders and conditions (differential diagnosis)
This section lists other disorders that should be considered in the differential diagnosis – 
particularly those that share presenting symptoms or features. For each of these disorders, this 
section describes the features that differentiate it from the index disorder, providing guidance to 
the clinician about how to make this differentiation. Issues related to the concurrent diagnosis 
of the disorder being distinguished from the index disorder are also discussed in this section. 
The boundary descriptions generally cover all information conveyed by exclusion terms on the 
ICD-11 MMS platform.3 Exclusion terms are often confusing to clinicians because they assume 
that they mean that the excluded condition cannot be diagnosed simultaneously with the index 
condition, which is not the case. Rather, an exclusion term in the ICD-11 MMS indicates that the 
condition excluded is not part of the condition described by the category, so that both conditions 
may be used at the same time if warranted. These considerations are covered more clearly and 
explicitly in the boundary descriptions found in this section of the CDDR.
Making an ICD-11 diagnosis using the CDDR
Consideration of essential (required) features
The diagnostic process starts with a consideration of whether the presentation meets the 
diagnostic requirements laid out in the essential (required) features section of the CDDR for 
the diagnosis under consideration. There are two types of essential features: those that must 
be present for the diagnostic requirements to be met and those that require a consideration of 
whether the symptoms may be better explained by other mental disorders that share presenting 
features. This aspect of the diagnostic evaluation includes a consideration of:
• particular symptoms that must be present (which may be expressed as a minimum number 
of symptoms from an item list – e.g. “Several of the following symptoms must be present”);
• the minimum amount of time that symptoms need to have been present (e.g. “present…for 
a period of at least several months”);
• frequency or proportion of the time that symptoms need to be present during that required 
period of time (e.g. “most of the time”, “most of the day, nearly every day”, “for more days 
than not”, “more than 1 hour per day”, “multiple incidents”);
3 ICD-11 for Mortality and Morbidity Statistics (ICD-11 MMS) [website]. Geneva: World Health Organization; 2023 (https://ICD.who.
int/browse11/l-m/en#/).

Clinical Descriptions and Diagnostic Requirements for ICD-11 Mental, Behavioural or Neurodevelopmental Disorders
• in some cases, whether the onset of symptoms meets a particular diagnostic requirement (e.g. 
“characterized by the rapid and concurrent onset of several characteristic symptoms”); and
• whether the symptoms meet any stated requirement regarding their impact on the individual’s 
functioning (“symptoms result in significant impairment in personal, family, social, 
educational, occupational or other important areas of functioning”) or have resulted in 
“significant distress”.
As noted, the CDDR generally avoid artificial precision in quantifying the exact number of items 
that must be present from a list of symptoms or specifying a precise duration requirement. Too 
rigidly applied, these can create barriers – for example, due to cultural variation or in contexts 
where an individual may have limited opportunities to access care. The essential features attempt 
to describe the relevant clinical phenomena clearly in order to allow for flexible application of 
the CDDR in establishing the presence of each diagnostic item. It is up to the diagnosing health 
professional to make a judgement about its presence or absence, considering the entire context 
of the clinical presentation. If the essential features do not mention a required duration for the 
symptoms, it is assumed that the symptoms should have been present for at least one month in 
order to assign the diagnosis. 
Consideration of other disorders that may share presenting features
This aspect of the diagnostic evaluation includes whether the symptoms are best considered 
to be a manifestation of a disease or disorder classified outside of the mental, behavioural and 
neurodevelopmental disorders chapter (e.g. a sleep-wake disorder, a disease of the nervous 
system, or another medical condition). In cases where the symptoms are judged to be a 
direct pathophysiological consequence of a medical condition and the mental, behavioural or 
neurodevelopmental symptoms are a specific focus of clinical attention, a diagnosis of one of 
the secondary mental or behavioural syndromes associated with disorders and diseases classified 
elsewhere may be assigned, in addition to the appropriate diagnosis for the etiological medical 
condition. For example, depressive symptoms similar to those of a depressive episode that are 
judged to be due to hypothyroidism would warrant a diagnosis of secondary mood syndrome, with 
depressive symptoms in addition to hypothyroidism. However, certain disorders are diagnosed 
regardless of whether they are believed to be caused by a medical condition classified elsewhere, 
including neurocognitive disorders and certain neurodevelopmental disorders (i.e. disorders of 
intellectual development, autism spectrum disorder, stereotyped movement disorder).
The evaluation also includes whether the symptoms are due to the effects of a substance or 
medication on the central nervous system. If so, a diagnosis of one of the substance-induced 
mental disorders (e.g. alcohol-induced delirium, amfetamine-induced psychotic disorder) is 
likely to be appropriate. Other categories specifically linked to substances or medications include 
catatonia induced by substances or medications; amnestic disorder due to psychoactive substances, 
including medications; and dementia due to psychoactive substances, including medications.
Finally, the diagnostic evaluation includes whether there are other ICD-11 mental, behavioural 
and neurodevelopmental disorders that share features with the disorder under consideration, 
that might better account for the symptomatic presentation. Whether a particular disorder that 
could account for the symptoms in fact better accounts for them is a clinical judgement. For 
example, the essential features of social anxiety disorder, which are characterized by marked and 
excessive fear or anxiety that occurs in social situations, includes the diagnostic requirement 
that “the symptoms are not better accounted for by another mental disorder (e.g. agoraphobia, 
body dysmorphic disorder, olfactory reference disorder)”. Each of these listed disorders may 
also involve the development of anxiety in social situations. For body dysmorphic disorder and 
olfactory reference disorder, the anxiety involves excessive self-consciousness about perceived 
defects in appearance or emitting an offensive body odour, respectively. In agoraphobia, the

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Using the CDDR for ICD-11 mental, behavioural and neurodevelopmental disorders in clinical settings
anxiety is related to a fear of specific negative outcomes in social situations, such as panic attacks 
or other incapacitating (e.g. falling) or embarrassing (e.g. incontinence) physical symptoms. In 
making the clinical judgement of whether the symptoms of anxiety in social situations are better 
accounted for by one of these other disorders, the clinician takes into account factors such as the 
temporal sequence of the symptoms, which symptoms predominate, and the presence of other 
clinical features.
Consideration of boundary with normality (threshold)
For the most part, mental disorders occur on a severity continuum with no sharp division 
separating cases and non-cases (i.e. normality), making the differentiation between a mild case 
of the disorder and non-disordered normal variation potentially challenging. It is advisable to 
review this section because, in some cases, what might appear to be evidence of psychopathology 
may in fact be within the bounds of normality given the individual’s developmental stage and 
cultural context. This section of the CDDR also points out common false-positive presentations.
Consideration of boundaries with other disorders and conditions 
(differential diagnosis)
This section of the CDDR is an extension and expansion of the “consideration of other 
disorders that may share presenting features” element of the essential features and provides 
a more comprehensive review of other disorders that should be considered in the differential 
diagnosis. The clinician should consider whether any of the disorders listed might explain the 
presenting symptoms.
Consideration of co-occurring and mutually exclusive diagnoses
ICD-11 diagnoses are generally assigned for every disorder for which the diagnostic requirements 
are met; that is, co-occurring diagnoses are typically permitted. However, there are specific 
situations in which the diagnostic requirements may be met for more than one disorder, typically 
because of symptom overlap, but the CDDR recommend making only a single diagnosis. In most 
cases, this is noted in the essential features but, in some cases, it is noted in the description of 
the differential diagnosis for that disorder in the section on boundaries with other disorders 
and conditions.
In the CDDR, recommendations against diagnosing two particular disorders together (i.e. cooccurrence) are generally made in one of the following ways.
• “The symptoms do not meet the diagnostic requirements for …”; “The symptoms do not 
occur exclusively during episodes of …”; “The individual has never met the diagnostic 
requirements for …”: these types of exclusionary statements are typically used if the 
symptomatic presentation of the disorder in question is already part of the definition of 
another disorder, and an additional diagnosis of the excluded disorder would be redundant.
• The first case (“symptoms do not meet diagnostic requirement for”) prevents the assignment 
of both diagnoses if the diagnostic requirements for both disorders are met at the same time, 
and generally indicates that the other disorder should be diagnosed instead. For example, 
the CDDR for bulimia nervosa indicate that the diagnosis should only be assigned if the 
symptoms do not meet the diagnostic requirements for anorexia nervosa, so that individuals 
who maintain an excessively low body weight by reducing their energy intake through purging 
behaviour would be assigned only a single diagnosis of anorexia nervosa rather than diagnoses 
of both anorexia nervosa and bulimia nervosa. The presence of bulimia-like behaviour is 
indicated with the binge-purge pattern specifier applied to the diagnosis of anorexia nervosa.