Classification & Assessment in Psychiatry · Paper A
Depression: diagnostic criteria (ICD-11)
ICD-11 requires at least one of two core symptoms, depressed mood or markedly diminished interest and pleasure, plus enough additional symptoms to reach 5 of 10 total, present for most of the day, nearly every day, for at least two weeks. Severity is graded not by a fixed symptom count but by combining symptom number, severity, and functional impairment together. Clinically, two patients who each hit the same symptom count can still land in different severity bands depending on how much daily function they retain.
The 10 symptoms span three clustersaffective (depressed mood, anhedoniaThe loss of the ability to feel pleasure from things that used to be enjoyable.Read more →, loss of interest or pleasure), cognitive-behavioural (poor concentration, low self-worth, hopelessness, recurrent thoughts of death), and neurovegetative (sleep disturbance, appetite change, psychomotorRelating to the link between mental state and physical movement, such as being visibly slowed down or agitated.Read more → change, a slowing or speeding of movement and thinking, low energy). Unlike ICD-10, ICD-11 abandons rigid symptom-count cut-offs for severity grading, instead integrating symptom number, severity, and functional impairment. Two patients meeting the same 6 of 10 symptoms can land in different severity bands, e.g. one still working full-time versus one unable to leave the house. In practice, functional impairment, not symptom count alone, drives which severity band a patient falls into.
A fresh MBBS graduate meets low mood constantly, but not every low mood is a depressive episode. ICD-11, the World Health Organization's (WHO) eleventh revision of the International Classification of Diseases, sets a specific bar so clinicians diagnose consistently across countries. Getting the criteria right matters because both over-diagnosis, labelling normal sadness as illness, and under-diagnosis, missing a treatable episode, cause real harm.
A depressive episode, under ICD-11, is a clinical diagnosis built from a specific combination of core and additional symptoms present for at least two weeks, not simply feeling sad. For example, imagine two junior doctors seeing the same tearful patient after a bereavement: one who knows the criteria correctly recognises normal grief, while one who does not may start unnecessary treatment.
ICD-11 requires at least one of two core symptoms to be present nearly every day, most of the day, for at least two weeks: depressed mood, or anhedonia (a markedly reduced ability to feel interest or pleasure in things a person used to enjoy). Without at least one of these two, a depressive episode cannot be diagnosed, no matter how many other symptoms are present. This is the anchor of the whole criteria set: everything else builds on top of this core requirement.
Beyond the core symptom, ICD-11 lists ten characteristic symptoms across three clusters. The affective cluster covers depressed mood and themselves. The cognitive-behavioural cluster covers poor concentration, low self-worth or excessive guilt, hopelessness, and recurrent thoughts of death or suicide. The neurovegetative cluster covers sleep disturbance (insomnia or hypersomnia), appetite or weight change, and change (a slowing or speeding of movement and thinking, sometimes visible as agitation or retardation). A diagnosis needs the total symptom count, including the core symptom, to reach five of these ten, sustained for the same two-week window.
Diagnosis is established entirely through structured clinical assessment: there is no blood test or scan (biomarker or imaging finding) that confirms a depressive episode. A clinician systematically works through the two core symptoms and the ten characteristic symptoms, confirming the duration (at least two weeks, nearly every day, most of the day) and ruling out an organic cause (such as hypothyroidism or medication side effects) or a substance-induced cause before settling on the diagnosis. A key change from ICD-10 is how ICD-11 grades severity: rather than using a rigid symptom-count cut-off for mild, moderate, and severe, ICD-11 integrates three things together: symptom number, symptom severity, and functional impairment. Consider a patient who meets six of the ten symptoms but is still working full-time and managing daily life reasonably well; that patient may be graded as mild-to-moderate. Another patient meeting the same six symptoms but unable to leave the house or care for themselves would be graded more severe. A severe episode may also carry a 'with psychotic symptoms' specifier when (fixed false beliefs), (perceptions with no real external stimulus), or depressive accompany the mood disturbance.
Several conditions mimic a depressive episode and must be ruled out as part of diagnosis. Dysthymic disorder is a chronic, lower-grade depressive picture lasting two years or more that never reaches full episode severity. Adjustment disorder with depressed mood involves subthreshold symptoms tightly linked to an identifiable stressor. Bipolar disorder in a current depressive episode requires a past hypomanic or manic episode somewhere in the history, which unipolar depression does not have. Normal grief centres on the loss itself and tends to fluctuate with reminders of the person, rather than pervading nearly every context of daily life the way a depressive episode does.
Putting the criteria together into a real diagnostic process: a clinician confirms at least one core symptom (depressed mood or ) present nearly every day for two weeks, counts additional symptoms from the ten-item list until reaching a total of five, checks that a physical or substance-related cause has been reasonably excluded, and then grades severity using symptom count, symptom severity, and functional impairment together rather than a rigid cut-off. This structured, criteria-based process is what separates an ICD-11 diagnosis from an informal impression of "seems depressed."
Once the diagnostic threshold is met, management follows a stepped approach. NICE (the UK's National Institute for Health and Care Excellence) guidance for mild-to-moderate depression favours starting with structured psychological therapy, such as cognitive behavioural therapy (CBT, a talking treatment that targets unhelpful thoughts and behaviours), before or alongside medication. For moderate-to-severe episodes, first-line treatment typically combines an antidepressant, most often a selective serotonin reuptake inhibitor (SSRI), with psychological therapy. The BNF (British National Formulary) provides the practical prescribing detail, including starting doses and monitoring requirements, for whichever antidepressant is chosen. Suicide risk assessment is a mandatory part of every review, since recurrent thoughts of death is one of the ten listed symptoms and can escalate quickly. Follow-up review, typically at two to four weeks after starting treatment, checks response and tolerability, and treatment usually continues for at least six months after remission to reduce relapse risk.
The classic trap is a vignette describing four or five weeks of low mood with several vegetative symptoms in a patient who is still coping reasonably well functionally: candidates who grade purely on symptom count alone will over-call severity, while the ICD-11 pearl is that function matters just as much as the number: the same symptom count can be mild-to-moderate in one patient and severe in another depending on how much daily life has broken down.
An ICD-11 depressive episode needs at least one of two core symptoms (depressed mood or ) plus enough additional symptoms to reach five of ten, sustained for two weeks, with severity graded by symptom count, severity, and function together rather than a fixed cut-off.