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Exploring depression
Exploring depression

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2.2 The diagnosis of depression

Boxes 5 and 6 briefly outline the criteria for a depressive episode according to the ICD-10 and DSM-IV-TR classification systems (ICD, 2003; APA, 2000). The DSM-5 criteria for major depressive disorder and persistent depressive disorder are summarised in Box 7. The 11th revision of the International Classification of Diseases (ICD-11 [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] ) became available on 18 June 2018 and has yet to be used more widely at the time of writing.

Depression is a broad and heterogeneous diagnosis. Low mood, loss of interest and pleasure in activities and loss of energy are among the key symptoms. Severity is determined by the number and severity of symptoms, as well as the degree of functional impairment (activities of daily living). Formal diagnosis of major depression requires at least four out of ten symptoms according to ICD-10 or at least five of the nine symptoms in the DSM (see Boxes 5-7). Symptoms should be present for at least two weeks, and at sufficient severity for most of every day. A depressive episode can be part of a lifetime pattern of disturbance associated with a diagnosis of recurrent depressive disorder, bipolar affective disorder or persistent affective disorder. Symptoms are considered persistent if they continue despite active monitoring or (low-intensity) intervention typically over a period of several months, and to meet the previous diagnosis of ‘dysthymia’, symptoms should be present for at least two years (NICE, 2018).

In DSM-5, what was previously termed ‘dysthymia’ now falls under the category of ‘persistent depressive disorder’ together with chronic major depressive disorder (see Box 7) (APA, 2013b). The reasoning behind this change was ‘an inability to find scientifically meaningful differences between these two conditions’ (APA, 2013b). The core criterion symptoms for a major depressive episode, and the specified duration of at least two weeks have not changed from the previous version (APA, 2013b).

In the UK, up until 28 June 2022, the National Institute for Health and Care Excellence (NICE) clinical guidelines for depression in adults (CG90 ‘Depression in adults: recognition and management’ published October 2009, replacing CG23 published in December 2004) still referred to both the ICD-10 and DSM-IV criteria. The NICE (CG90) guideline stated that:

…..classificatory systems are agreed conventions that seek to define different severities of depression in order to guide diagnosis and treatment, and their value is determined by how useful they are in practice. After careful review of the diagnostic criteria and the evidence, the Guideline Development Group decided to adopt DSM-IV criteria for this update rather than ICD-10, which was used in the previous guideline (NICE clinical guideline 23). This is because DSM-IV is used in nearly all the evidence reviewed and it provides definitions for atypical symptoms and seasonal depression. Its definition of severity also makes it less likely that a diagnosis of depression will be based solely on symptom counting. In practical terms, clinicians are not expected to switch to DSM-IV but should be aware that the threshold for mild depression is higher than ICD-10 (five symptoms instead of four) and that degree of functional impairment should be routinely assessed before making a diagnosis. Using DSM-IV enables the guideline to target better the use of specific interventions, such as antidepressants, for more severe degrees of depression.

(NICE, 2018)

It is important to bear in mind that clinical guidelines are also periodically reviewed and revised in line with diagnostic classification systems and may therefore be subject to change over time. CG90 has since been updated and was replaced by NICE guideline NG222 ‘Depression in adults: treatment and management’, published on 29 June 2022.

NG222 now refers to both DSM-5 and ICD-11, and places greater emphasis on informed and shared (healthcare professional-service user) decision-making with regards to choice and preference of treatment options. This includes ‘carrying out an assessment of need; developing a treatment plan; taking into account any physical health or co-existing mental health problems; discussing factors that would make the person most likely to engage with treatment; taking previous treatment history into account; addressing any barriers to the delivery of treatments due for example to disabilities, language or communication difficulties; ensuring regular liaison between healthcare professionals in specialist and non-specialist settings; and matching the choice of treatment to meet the needs and preferences of the person with depression, using the least intrusive and most resource efficient treatment that is appropriate for their clinical needs or that has worked for them in the past’ (NG222, Section 1.4.1 and 1.4.2).

Box 5 ICD-10 criteria for diagnosis of a depressive episode

(based on ICD-10, 2003)

In typical mild, moderate, or severe depressive episodes, the patient suffers from lowering of mood, reduction of energy, and decrease in activity. Capacity for enjoyment, interest, and concentration is reduced, and marked tiredness after even minimum effort is common. Sleep is usually disturbed and appetite diminished. Self-esteem and self-confidence are almost always reduced and, even in the mild form, some ideas of guilt or worthlessness are often present. The lowered mood varies little from day to day, is unresponsive to circumstances and may be accompanied by so-called "somatic" symptoms, such as loss of interest and pleasurable feelings, waking in the morning several hours before the usual time, depression worst in the morning, marked psychomotor retardation, agitation, loss of appetite, weight loss, and loss of libido. Depending upon the number and severity of the symptoms, a depressive episode may be specified as mild, moderate or severe.

(F32 Depressive Episode: ICD-10 2003). a

Key symptoms

At least one of the following, most days, most of the time for at least two weeks:

  • persistent sadness or low mood, and/or

  • loss of interests or pleasure

  • fatigue or low energy.

If any of the above are present, the individual is then asked about associated symptoms:

  • disturbed sleep

  • poor concentration or indecisiveness

  • low self-confidence

  • poor or increased appetite

  • suicidal thoughts or acts

  • agitation or slowing of movements

  • guilt or self-blame.

The 10 symptoms then define the ‘degree’ of depression and management is based on the particular degree:

  • not depressed (fewer than four symptoms)

  • mild depression (four symptoms)

  • moderate depression (five to six symptoms)

  • severe depression (seven or more symptoms, with or without psychotic symptoms).

Symptoms should be present for a month or more and every symptom should be present for most of every day.


Note [a] F32 major depressive disorder, single episode excludes: bipolar disorder (F31), manic episode (F30) and recurrent depressive disorder (F33).

Box 6 Diagnostic criteria for major depressive episode

(based on DSM-IV-TR, APA, 2000)

A diagnosis of depression is suggested if, during the same two-week period, a person experiences five (or more) of the following symptoms, which must include either or both of the key presenting symptoms.

At least one of the following key symptoms:

  • persistent feelings of depressed mood (determined either by subjective report or observation made by others)

  • loss of interest or pleasure in usual activities.

Plus three or more of the following symptoms:

  • changes in appetite that result in weight losses or gains not related to dieting

  • insomnia or oversleeping

  • loss of energy or increased fatigue

  • restlessness or irritability

  • feelings of worthlessness or inappropriate guilt

  • difficulty thinking, concentrating or making decisions

  • thoughts of death or suicide or attempts at suicide.

Symptoms should not be counted if they are a direct physiological effect of a substance (drug abuse or medication); or a medical condition (e.g. hypothyroidism); or if they would be better accounted for by bereavement (i.e. after the loss of a loved one).

Box 7 DSM-5 criteria for major depressive disorder and persistent depressive disorder

(based on APA, 2013a)

Major depressive disordera

Five or more of nine symptoms (including at least one of depressed mood and loss of interest or pleasure) in the same two- week period; each of these symptoms represents a change from previous functioning:

  • depressed mood (subjective or observed)

  • loss of interest or pleasure

  • change in weight or appetite

  • insomnia or hypersomnia

  • psychomotor retardation or agitation (observed)

  • loss of energy or fatigue

  • feelings of worthlessness or guilt

  • impaired concentration or decisiveness

  • thoughts of death or suicidal ideation or suicide attempt.

Persistent depressive disorderb

Depressed mood for most of the day, for more days than not, for two years or longer.

Presence of two or more of the following during the same period:

  • poor appetite or overeating

  • insomnia or hypersomnia

  • low energy or fatigue

  • low self-esteem

  • impaired concentration or indecisiveness

  • hopelessness.


Never without symptoms for more than two months.

Note [a] in children and adolescents, mood can be irritable.

Note [b] in children and adolescents, mood can be irritable and duration must be one year or longer.