How an ICD-11 Diagnosis Works: A Step-by-Step Guide
An ICD-11 diagnosis is a structured process of reasoning that leads from a person's reported difficulties to an accurate diagnosis. In this guide we walk through that process step by step, from the first conversation to recording the diagnosis in the clinical notes.
What ICD-11 is and what this guide covers
ICD stands for the International Classification of Diseases. It is a global catalogue of disease entities maintained by the World Health Organization, the specialised United Nations agency responsible for health. The eleventh revision, designated ICD-11, has replaced the earlier ICD-10 version and is today the official international standard for describing diseases.
Mental, behavioural and neurodevelopmental disorders are described in Chapter 6 of ICD-11. That is the area this guide addresses. Rather than presenting a list of disorders, we show the process itself: how a clinician moves from a patient's clinical picture to a diagnosis in line with the logic of ICD-11 diagnostics.
It is worth marking a clear boundary from the outset. The classification organises knowledge and provides a shared language, but it does not replace contact with a specialist. A diagnosis is always made by a qualified clinician on the basis of a full assessment, never by a single tool, a questionnaire, or by reading a description of symptoms.
Diagnosis in mental health does not consist of mechanically matching a patient to a table. It is a process of clinical reasoning in which a specialist gathers information, organises it, considers possible explanations, and only then formulates a conclusion. The sections that follow describe this process stage by stage.
Step one: presentation and clinical picture
Everything begins with the presentation. A patient comes in with specific difficulties: low mood, anxiety, sleep problems, intrusive thoughts, a change in behaviour, or the concern of relatives. At this stage the clinician's task is to listen and build a complete picture, not to name the problem in haste.
The clinical picture is the whole of what a specialist establishes through conversation and observation. It comprises the complaints reported, the symptoms visible during the meeting, their severity, duration, time of onset, and their impact on everyday functioning: at work, in education, in relationships and in independent self-care.
Already at this stage it is important to distinguish a symptom from an experience. Sadness, anxiety or tension are natural parts of human life. They become the subject of diagnostic assessment only when their severity, duration or nature goes beyond what is understandable in the given situation.
A good clinical picture is also set within the person's history. The clinician asks about earlier episodes, treatment, physical illnesses, medications taken, substance use, and the family and occupational situation. This information will be needed at later stages, particularly during differential diagnosis.
Step two: history-taking and the mental state examination
The basic tool of ICD-11 diagnostics is the clinical conversation, that is, a structured interview. The specialist asks not only what is wrong, but also when it began, how it has developed, what worsens or eases the symptoms, and how the person coped previously. The interview also covers life history, relationships, work and earlier treatment.
Conducted alongside it is the mental state examination: a structured observation of speech, mood, the flow of thinking, the content of experiences, attention, memory and insight (awareness of one's own difficulties). It makes it possible to notice what a patient may not report directly.
Part of this step is also a safety assessment. The clinician checks whether there is any threat to life or health, including suicidal thoughts or a risk of harm. This is a priority that takes precedence over the further diagnostic stages if the situation requires it.
The interview is sometimes supplemented with information from relatives, with earlier medical records, and, where indicated, with screening tools and questionnaires. These tools do not make a diagnosis; they only indicate that a given area is worth examining more closely.
Step three: an initial ordering of the picture
With the information gathered, the clinician begins to organise it. The first question is: which group of disorders does this picture fit. Chapter 6 of ICD-11 divides disorders into related groups: mood, anxiety or fear-related, psychotic, stress-related, feeding and eating, neurocognitive, and others.
The structure of the classification itself helps at this step. The codes for disorders are arranged hierarchically, and entities that lie close to one another often share features of the clinical picture. For example, mood disorders have codes beginning with 6A6, and anxiety or fear-related disorders begin with 6B0. The clinician therefore moves across a map of relationships rather than a random list.
At this stage an initial set of hypotheses is formed: several diagnoses that provisionally fit the picture. This is not yet a diagnosis but a list of candidates for further checking. A good clinician deliberately keeps several possibilities open at once, rather than becoming attached to one too early.
Ordering the picture also includes assessing the time axis: when the symptoms began, whether they built up gradually or appeared in episodes, whether this is a first occurrence or a recurrence. The course over time is one of the key elements distinguishing one disorder from another.
Step four: referring to the CDDR guidelines
At the heart of ICD-11 diagnostics is the document accompanying Chapter 6: the CDDR, the Clinical Descriptions and Diagnostic Requirements. It is this document that the clinician uses when checking whether a patient's picture corresponds to a specific disorder.
For each disorder, the CDDR provides a recurring set of elements. First a clinical description, that is, an overall picture written in accessible language. Then the essential features, the symptoms and conditions that must be present for a given diagnosis to be considered at all. Next come the boundary with normality, the boundary with other disorders, and information about the course, age, sex and cultural context.
ICD-11 deliberately moves away from rigidly counting symptoms, of the so-and-so-many points from a list kind. Instead, the clinician assesses whether a patient's picture corresponds to the described pattern of essential features. This approach is more flexible but also more demanding: it is not enough to tick off symptoms, one has to assess whether the defining core of the disorder is present.
For example, to consider generalised anxiety disorder (code 6B00), the essential feature is persistent, excessive and difficult-to-control anxiety or worry concerning many areas of life. Symptoms such as muscle tension or sleep problems reinforce the picture, but they do not replace this core feature. Similarly, in schizophrenia (6A20) the essential features are specific psychotic symptoms persisting for the required period of time.
Step five: checking the threshold for a disorder
Meeting the description of the symptoms is not everything. In many places ICD-11 requires that the symptoms lead to significant distress or to impairment of functioning in important areas of life. This condition serves as a threshold that separates a disorder from an ordinary, if difficult, human reaction.
Functioning is the ability to cope at work or in education, in family and social relationships, and in independent daily activity. The clinician assesses whether the symptoms genuinely disrupt any of these areas. Features that do not cause distress and do not make life harder usually do not justify a diagnosis.
Distress and impaired functioning are two separate, though related, conditions. Sometimes a person suffers despite coping well outwardly; sometimes functioning is clearly disturbed while the sense of distress is limited. ICD-11 generally regards the presence of either of these elements as significant.
This step guards against the over-medicalisation of ordinary life. Fear of a real threat, sadness after a loss, or tension before a difficult event are natural reactions. A diagnosis is justified only when the reaction clearly exceeds what is understandable and genuinely makes functioning harder.
Step six: differential diagnosis
The intellectually most important stage is differential diagnosis, that is, considering and ruling out alternative explanations for the same clinical picture. Many mental health symptoms are non-specific: the same symptom appears in different disorders, so its mere presence does not point to a diagnosis.
Low mood is a good example. It may indicate single episode depressive disorder (code 6A70) or recurrent depressive disorder (6A71), but also the depressive phase of bipolar type I disorder (6A60), a reaction to severe stress in the form of adjustment disorder (6B43), or the effect of a physical illness or of a substance. The clinician must determine which explanation fits best.
Anxiety, likewise, accompanies generalised anxiety disorder (6B00), panic disorder (6B01), social anxiety disorder (6B04) and post-traumatic stress disorder (6B40) alike. The CDDR supports differential diagnosis by providing, for each disorder, separate notes on the boundaries with related entities.
A separate, mandatory step is ruling out physical causes and the effect of substances. Mental health symptoms may result from general medical conditions, from medications, or from the use of psychoactive substances, including alcohol (disorders due to alcohol use have code 6C40). ICD-11 also provides separate categories for secondary mental syndromes, for example secondary mood syndrome (6E62), where the symptoms are a direct consequence of another illness.
Step seven: specifying severity and course
Once the leading diagnosis becomes clear, the clinician refines its picture. Here ICD-11 uses qualifiers, that is, additional designations describing severity and course. They make it possible to record not only which disorder was diagnosed, but also how severe the picture is.
The most common qualifier is severity. Many disorders are described as mild, moderate or severe; this is the case, for example, with a depressive episode within the mood disorders. This distinction has real significance for planning further care, because a mild and a severe picture call for different management.
The second important qualifier is course. ICD-11 distinguishes a first episode from a recurrent state, and a symptomatic phase from partial or full remission. This is clearly visible in the detailed code structure for schizophrenia (6A20), where successive characters of the code specify whether it is a first episode, multiple episodes or a continuous course, and what the current state is.
This approach is connected with a broader change in ICD-11: a strengthening of the dimensional approach, which describes a disorder by the intensity of features on a scale rather than as a closed pigeonhole. It is seen most fully in personality disorder (code 6D10), where severity is assessed first and prominent traits are described only afterwards.
Step eight: formulating and recording the diagnosis
The outcome of the whole process is the formulation of a diagnosis. The clinician combines the chosen entity with the appropriate severity and course qualifiers, obtaining a full record: a code together with any extensions after the decimal point. The code ensures unambiguity: the same record will be understood in the same way by another specialist.
ICD-11 diagnostics also allows more than one diagnosis. In clinical practice, co-occurrence, the presence of several disorders in the same person, is common. If the picture requires it, the clinician records several diagnoses, and additional categories make it possible to specify the course or modifying features.
A diagnostic formulation, however, is more than the code alone. Good practice includes a description of the clinical picture, of the factors maintaining the difficulties, of the person's strengths, and of the life context. Such a description translates into a concrete plan of care far better than a code designation on its own.
The diagnosis then becomes the basis of the conversation with the patient. Explaining what the diagnosis means, what the expected course is, and what the options for help are, is an integral part of the diagnostic process, not an addition to it.
Step nine: reviewing the diagnosis over time
A diagnosis is neither a one-off act nor a verdict. A patient's picture changes over time, and new information may cast earlier conclusions in a different light. For this reason good practice treats a diagnosis as a working conclusion open to revision.
Review is especially important where the early picture tends to be ambiguous. A state initially described as a depressive episode may over time reveal an episode of hypomania or mania, which shifts the diagnosis towards bipolar disorder. Observing the course is decisive here.
Review guards against two opposite errors: hastily assigning a diagnosis, and overlooking a disorder that requires attention. The clinician returns to earlier hypotheses if the course does not confirm the original diagnosis.
The element of course is, in any case, built into the classification itself. Phase qualifiers, episode, partial remission, full remission, make it possible to record changes of state over time and to track how the patient responds to treatment. Diagnosis and observation are therefore interwoven.
The role of digital tools and educational materials
The digital form of ICD-11 makes the classification more accessible than it once was. Alongside the official World Health Organization platform, supporting tools are being developed that organise knowledge about disorders, their codes, symptoms and relationships, making it easier to navigate Chapter 6.
Tools of this kind can support learning and practice; they help to find the description of a disorder quickly, to compare related entities and to trace differential diagnosis. They remain, however, a support and not a substitute for clinical assessment. Diagnostic value arises only in combination with knowledge, experience and direct contact between the clinician and the patient.
For people outside health care, patients, their relatives, students or those interested in the subject, materials about ICD-11 diagnostics serve an educational role. They make it possible to understand how a given disorder is thought about, which reduces the anxiety arising from a lack of knowledge and makes conversation with a specialist easier.
One overriding principle applies here: a description is not a diagnosis. Recognising symptoms in oneself or in someone close on the basis of reading does not replace clinical assessment. If symptoms cause concern, the appropriate step is to contact a specialist, and in a situation of threat to life or health, to seek urgent help without delay.