Patient Health Questionnaire (PHQ-9)

The PHQ-9 is a nine item self-report questionnaire that screens for depression and measures its severity over the preceding two weeks. Each item is scored from 0 (not at all) to 3 (nearly every day), giving a total from 0 to 27.

It is a screening and monitoring tool. A score does not diagnose depression, and the diagnosis requires a structured clinical interview.

Usage. It is used in primary care, perinatal services, and specialist mental health settings, and to monitor response over time.

Indications. Screening in patients with symptoms suggestive of depression, routine monitoring of known depression, and assessment of response over time.

Preparation and technique. The patient completes the questionnaire in private, ideally in a language they understand. The clinician reviews each item, particularly the question on thoughts of self-harm or death, and documents any safety concern.

Contraindications and precautions. The questionnaire is less reliable in people with cognitive impairment or limited literacy, and in those with acute psychosis or severe distress. Clinical judgement decides its use in these groups.

Interpretation.

• Scores of 0 to 4 indicate minimal symptoms.
• Scores of 5 to 9 indicate mild symptoms.
• Scores of 10 to 14 indicate moderate symptoms.
• Scores of 15 to 19 indicate moderately severe symptoms.
• Scores of 20 to 27 indicate severe symptoms.

Causes of a raised score. Depressive disorder, bipolar disorder, anxiety, medical illness, medication effects, and substance use.

Critical values and findings needing immediate action.

• A positive response to the self-harm question, indicating thoughts of self-harm or death, requires a same day suicide risk assessment by a clinician.
• A high total score with functional impairment requires prompt clinical review and a structured interview.

Limitations and artefacts. The score is affected by somatic symptoms in medical illness, which can overstate depression. The two week recall period can miss episodes. Cultural differences in expression of mood affect responses.

Follow up tests. A structured clinical interview to confirm the diagnosis, thyroid function tests, full blood count, and renal and liver function where medical causes are possible.

Special groups. Pregnancy and the postnatal period have their own screening tools, and the PHQ-9 is one part of the assessment. Older adults may under report somatic symptoms, and adolescents may need a different approach to interpretation.