How should I assess the severity of depression in a patient presenting with low mood?

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 ¹. This assessment should consider the severity of symptoms, previous history, duration, and course of the illness ¹. 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 ¹,².

A comprehensive assessment should involve discussing how various factors may have influenced the development, course, and severity of their depression ¹. 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 ¹.

Severity is broadly categorised based on symptoms and functional impairment:

• Subthreshold depressive symptoms: Fewer than five symptoms of depression ².
• Mild depression: Few, if any, symptoms beyond the five required for diagnosis, resulting in only minor functional impairment ².
• Moderate depression: Symptoms and functional impairment fall between 'mild' and 'severe' ².
• Severe depression: Most symptoms are present, and they markedly interfere with functioning, potentially with or without psychotic symptoms ².

Validated depression questionnaires, such as the PHQ-9, can be used to assess depression, symptom severity, and treatment response ³. 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 ¹.

Always directly ask people with depression about suicidal ideation and intent ¹. 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 ¹. 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 ¹,³.