How is major depressive disorder diagnosed?

How Major Depressive Disorder is Diagnosed

Major depressive disorder is diagnosed through a clinical assessment based on DSM-5 or ICD-10 criteria, requiring at least 5 specific symptoms (including depressed mood or anhedonia) lasting ≥2 weeks with functional impairment, supplemented by standardized screening tools like the PHQ-9, and confirmed through direct patient and family interviews. 1, 2

Diagnostic Criteria Framework

The diagnosis requires meeting specific DSM-5 criteria 1, 2:

• Core symptoms (must have at least one):

  • Depressed mood most of the day, nearly every day
  • Markedly diminished interest or pleasure in activities (anhedonia)

• Additional symptoms (need ≥4 more from this list):

  • Significant weight change or appetite disturbance
  • Insomnia or hypersomnia
  • Psychomotor agitation or retardation
  • Fatigue or loss of energy
  • Feelings of worthlessness or excessive guilt
  • Diminished ability to concentrate or indecisiveness
  • Recurrent thoughts of death or suicidal ideation

• Duration: Symptoms must persist for at least 2 weeks 2

• Functional impairment: Must cause clinically significant distress or impairment in social, occupational, or other important areas 1

Screening and Assessment Process

Initial Screening

Use standardized depression screening instruments 1, 3:

• PHQ-9 (9 items): Assesses DSM-IV major depressive disorder symptoms and functional impairment 3
• HAM-D (17 items): Clinician-administered scale; scores 7-17 suggest mild, 18-24 moderate, ≥25 severe depression 3
• BDI (21 items): Scores ≥20 suggest clinical depression 3
• HADS (14 items): Score ≥8 on depression scale indicates caseness; excludes physical symptoms 3

Critical caveat: A positive screening result alone does not establish the diagnosis of MDD, particularly in low-risk populations where positive predictive value may be low 1. Screening identifies who needs full diagnostic assessment.

Comprehensive Diagnostic Assessment

The assessment must include 1:

1. Direct clinical interview with the patient to systematically evaluate DSM-5 criteria—standardized instruments aid but do not replace clinical judgment 1

2. Collateral information from family members, caregivers, or teachers to corroborate symptoms and functional impairment 1

3. Functional impairment assessment across multiple domains:

   • School or work performance
   • Home functioning
   • Peer and social relationships
   • Subjective distress 1

4. Comorbidity screening: Assess for other psychiatric conditions (anxiety disorders, substance use, bipolar disorder) that commonly co-occur and affect treatment 1

5. Safety assessment: Always evaluate suicide risk, including ideation, plan, intent, and recent attempts 1

Recognizing Atypical Presentations

Adolescents and some adults may not clearly identify depressed mood as their chief complaint 1. Watch for these presenting symptoms that may signal MDD:

• Irritability (especially in younger patients)
• Fatigue
• Sleep disturbances (insomnia or hypersomnia)
• Weight changes
• Decline in academic or work functioning
• Family conflict
• Frequent somatic complaints 1

Important distinction: Patients who deny low mood but have anhedonia plus ≥4 other symptoms can still meet MDD criteria, though research suggests they may have briefer, less severe episodes with less suicidality 4.

Risk Factor Identification

Target assessment toward high-risk individuals 1:

• Previous personal or family history of depression, bipolar disorder, or suicide-related behaviors
• Other psychiatric illness or substance use history
• Significant psychosocial stressors (trauma, abuse, neglect, family crises)
• Frequent somatic complaints
• Foster care or adoption status

Severity Classification

Classify severity based on symptom count, intensity, and functional impairment 1:

• Mild: 5-6 symptoms of mild intensity with minimal functional impairment
• Moderate: Between mild and severe presentations
• Severe: All 9 DSM-5 symptoms present, OR severe functional impairment (unable to leave home), OR presence of suicide plan/intent/recent attempt, OR psychotic symptoms 1

Medical Differential

Before finalizing MDD diagnosis, rule out medical causes of depressive symptoms 3:

• Unrelieved pain or fatigue
• Delirium from infection or electrolyte imbalance
• Medication side effects
• Endocrine disorders (hypothyroidism)

The diagnosis is clinical and requires systematic evaluation—no laboratory test can confirm or exclude MDD 2. While emerging research explores biomarkers like plasma metabolomics 5 or neuroimaging 6, 7, these remain investigational and are not part of standard diagnostic practice.