Diagnostic Criteria for Major Depressive Disorder

Initial Screening and Diagnostic Assessment

The American College of Physicians recommends using the PHQ-9's nine questions as the primary diagnostic framework, starting with the two core symptoms of depressed mood and anhedonia, then proceeding to the remaining seven symptoms if either core symptom is present 1
A diagnosis of major depressive disorder requires at least 5 of the 9 symptoms present during the same 2-week period, with at least one being either depressed mood or loss of interest/pleasure, as per the Journal of Clinical Oncology guidelines 2
The symptoms must cause clinically significant distress or functional impairment, and the assessment of functional impairment is crucial in determining the diagnosis 2

The PHQ-9 loses accuracy in patients with cognitive impairment, and alternative assessment methods should be used in this population, according to Praxis Medical Insights 1
For elderly patients, the Geriatric Depression Scale (GDS-15) is recommended, which focuses on affective symptoms and excludes somatic items that may be confounded by medical illness, as suggested by the Journal of Clinical Oncology 3
It is essential to rule out medical causes before diagnosing major depressive disorder, including uncontrolled pain, fatigue, delirium from infection or electrolyte imbalance, thyroid disorders, or medication side effects, as per the Journal of Clinical Oncology guidelines 2, 3

The suicidal ideation question should never be skipped, as omitting it artificially lowers scores and misses critical risk information, according to Praxis Medical Insights 1
If any self-harm ideation is endorsed, immediate referral for emergency psychiatric evaluation is required, regardless of the total score, as recommended by Praxis Medical Insights 1