When assessing the severity of depression in a patient presenting with low mood, a comprehensive assessment is required that does not rely solely on a symptom count NICE NG222. This assessment should consider the severity of symptoms, previous history, duration, and course of the illness NICE NG222. It is crucial to also take into account the degree of functional impairment and/or disability associated with the possible depression and the length of the episode NICE NG222,NICE CG91.
A comprehensive assessment should involve discussing how various factors may have influenced the development, course, and severity of their depression NICE NG222. These factors include any history of depression, coexisting mental or physical disorders, past mood elevation (to rule out bipolar disorder), previous treatment experiences and responses, personal strengths and resources (including supportive relationships), interpersonal relationship difficulties, current lifestyle (e.g., diet, physical activity, sleep), recent or past stressful or traumatic life events, living conditions, drug and alcohol use, debt, employment situation, loneliness, and social isolation NICE NG222.
Severity is broadly categorised based on symptoms and functional impairment:
- Subthreshold depressive symptoms: Fewer than five symptoms of depression NICE CG91.
- Mild depression: Few, if any, symptoms beyond the five required for diagnosis, resulting in only minor functional impairment NICE CG91.
- Moderate depression: Symptoms and functional impairment fall between 'mild' and 'severe' NICE CG91.
- Severe depression: Most symptoms are present, and they markedly interfere with functioning, potentially with or without psychotic symptoms NICE CG91.
Validated depression questionnaires, such as the PHQ-9, can be used to assess depression, symptom severity, and treatment response NICE CKS. In guidelines, less severe depression (subthreshold and mild) is defined as scoring less than 16 on the PHQ-9 scale, while more severe depression (moderate and severe) is defined as scoring 16 or more NICE NG222.
Always directly ask people with depression about suicidal ideation and intent NICE NG222. If there is a risk of self-harm or suicide, assess social support, arrange appropriate help, and advise the person on how to seek further help if their situation deteriorates NICE NG222. Urgent referral to specialist mental health services is necessary if a person with depression presents a considerable immediate risk to themselves or others, or has more severe depression with significant risk of self-harm, suicide, harm to others, or self-neglect NICE NG222,NICE CKS.