What investigations and International Classification of Diseases (ICD) tools should I use to evaluate a patient presenting to primary care for a mental health referral, considering their demographic, medical history, and presenting symptoms?

Primary Care Mental Health Evaluation: Investigations and Screening Tools

Initial Screening Approach

Use the PHQ-9 (Patient Health Questionnaire-9) as your primary screening tool for depression, and the GAD-7 (Generalized Anxiety Disorder-7) for anxiety disorders. 1, 2 These are the most validated, efficient instruments for primary care settings, taking less than 5 minutes to administer and demonstrating excellent psychometric properties. 1, 3

Two-Step Screening Strategy

• Start with ultra-brief screens (PHQ-2 and GAD-2) consisting of just two questions each 1, 2, 3
• PHQ-2 asks about: (1) depressed mood and (2) anhedonia over the past 2 weeks, scored 0-3 for each item 1
• GAD-2 asks about: (1) feeling nervous/anxious and (2) inability to control worrying over the past 2 weeks 1
• If PHQ-2 ≥3 or GAD-2 ≥3, complete the full PHQ-9 or GAD-7 respectively 1, 2, 3

Depression Assessment Tools

PHQ-9 Scoring and Interpretation

• Cutoff score ≥10 has 88% sensitivity and 88% specificity for major depression 2, 4
• Score ranges indicate severity: 1-4 (minimal), 5-9 (mild), 10-14 (moderate), 15-19 (moderately severe), 20-27 (severe) 2, 4
• Some guidelines recommend ≥8 as cutoff in specific populations, though ≥10 is traditional 2
• Item 9 specifically assesses suicidal ideation and must be evaluated separately regardless of total score 1, 2

Critical Caveat About Screening

A positive screen does NOT establish diagnosis—it only identifies patients requiring further evaluation. 1, 2 In primary care populations with 5-10% depression prevalence, positive predictive value is only 24-40%, meaning 60-76% of positive screens are false positives. 1, 2 You must conduct a direct clinical interview using DSM-5 criteria to confirm diagnosis. 1, 2

Anxiety Assessment Tools

GAD-7 for Generalized Anxiety

• Cutoff score ≥10 indicates clinically significant anxiety requiring further evaluation 1, 3
• Detects not only GAD but also: panic disorder, social anxiety disorder, and PTSD with good sensitivity 3
• Score ranges: 5 (mild), 10 (moderate), 15 (severe) anxiety 1

Mini-SPIN for Social Anxiety Disorder

• Three-item tool specifically for social phobia 1, 5
• Cutoff score ≥6 has 89% sensitivity and 90% specificity 1, 5
• Use when patient reports: fear of social situations, performance anxiety, or avoidance of social interactions 5

Laboratory Investigations

Baseline Testing Before Treatment

Order these labs on all patients before initiating antidepressant treatment: 2

• Thyroid-stimulating hormone (TSH) to rule out thyroid-induced depression 2
• Complete blood count (CBC) 2
• Comprehensive metabolic panel (electrolytes, glucose, renal function, liver function) 2
• Liver function tests specifically before medication initiation 2

Targeted Testing Based on Risk Factors

Do NOT order extensive routine laboratory batteries without clinical indication—this yields mostly false positives (8 times more common than true positives). 2 Instead, order additional tests only when:

• First psychiatric presentation or new symptoms: Consider expanded workup 2
• Elderly patients: Add ECG, chest X-ray, BUN, vitamin B12 2, 6
• Gastrointestinal disorders (IBD, malabsorption, gastric surgery): Check vitamin B12 6
• Chronic medication use: B12 if on metformin, PPIs, or H2 blockers 6
• Substance abuse history: Targeted screening based on substances used 2
• Weight loss >5% or appetite changes in older adults: Nutritional assessment including B12 6

Comprehensive Clinical Assessment

Direct Interview Components

After positive screen, conduct structured interview assessing: 1

• Core depressive symptoms: Depressed mood, anhedonia, sleep changes, appetite/weight changes, fatigue, concentration problems, psychomotor changes, guilt/worthlessness 1
• Duration and persistence: Symptoms present most of the day, nearly every day for ≥2 weeks 1
• Functional impairment: Specific deficits in school/work, home, peer relationships 1
• Suicidal ideation: Plans, intent, access to means, protective factors 1, 2

Mandatory Comorbidity Screening

Screen for these conditions as they affect diagnosis and treatment: 1

• Bipolar disorder risk: History of manic/hypomanic episodes (use Mood Disorder Questionnaire if suspected) 7
• Anxiety disorders: Often comorbid with depression 1, 3
• Substance use disorders: Alcohol (AUDIT-C), opioids (Opioid Risk Tool) 1
• PTSD: Trauma history and re-experiencing symptoms 3
• Psychotic symptoms: Hallucinations, delusions 1

Collateral Information

• Obtain information from family members or caregivers when possible to corroborate symptoms and functional impairment 1
• Contact teachers or employers if academic/occupational decline is reported 1

Action Algorithm Based on PHQ-9 Score

Mild Symptoms (PHQ-9: 1-7)

• Provide psychoeducation about depression and normal stress responses 2
• Assess coping skills and resources 2
• Schedule reassessment at future visits, especially if risk factors present 2

Moderate Symptoms (PHQ-9: 8-14)

• Evaluate detailed history: Family history, previous episodes, trauma, psychosocial stressors 2
• Consider referral to psychology or psychiatry for diagnostic evaluation and treatment 2
• May initiate treatment in primary care if comfortable and systems support available 1

Moderate-to-Severe/Severe (PHQ-9: 15-27)

• Immediate referral to psychology and/or psychiatry mandatory 2
• Emergency intervention required if specific plans or intent for self-harm endorsed 1, 2
• Establish safety plan: Restrict lethal means, engage concerned third party, create emergency communication mechanism 1

Common Pitfalls to Avoid

• Never diagnose based on screening scores alone—false-positive rates are 60-76% in primary care 1, 2
• Don't overlook comorbid conditions (anxiety, substance use, PTSD) that fundamentally alter treatment approach 1, 2
• Avoid ordering extensive lab panels without indication—yields 8:1 ratio of false to true positives 2
• Don't skip Item 9 assessment—suicidal ideation requires immediate evaluation regardless of total PHQ-9 score 1, 2
• Never assume screening instruments work equally across cultures—local adaptation may be necessary for diverse populations 1
• Don't forget to assess functional impairment—diagnosis requires clinically significant impairment, not just symptom presence 1

Practice Systems Requirements

Screening is only beneficial when coupled with adequate systems for: 1

• Accurate diagnosis following positive screens 1
• Effective treatment (medication and/or psychotherapy) 1
• Careful follow-up and monitoring 1
• Referral pathways to mental health specialists 1