Define the clinical problem
Summarize the presenting concerns, time course, functional change, safety issues, and the patient’s priorities before naming a disorder.
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Metropolitan General Health System
PMHNP Clinical Learning Environment
Clinical Reasoning Resource
Diagnostic Reasoning & Clinical Formulation
Diagnostic reasoning identifies and compares plausible explanations for the presentation. Clinical formulation goes further: it creates a concise, evidence-based understanding of how the patient's symptoms, history, health, relationships, environment, strengths, and current circumstances fit together—and how that understanding should shape care.
Reasoning process
Move from information to a defensible clinical understanding
Clinical reasoning is iterative. New information may strengthen, weaken, reorder, or replace an earlier hypothesis.
Organize the evidence
Integrate history, mental status, medical findings, medications, substances, sleep, development, trauma, culture, collateral, and longitudinal pattern.
Generate a differential
Consider plausible psychiatric, substance- or medication-induced, medical, neurologic, developmental, sleep-related, and contextual explanations.
Compare competing explanations
Identify the evidence supporting and weakening each possibility, important missing information, and findings that cannot safely be ignored.
Prioritize and commit
Name the leading diagnosis or working hypothesis, meaningful alternatives, and cannot-miss conditions using calibrated—not falsely certain—language.
Build the formulation
Explain how vulnerabilities, triggers, maintaining factors, strengths, and protective factors interact in this person at this time.
Connect reasoning to action
Let the formulation guide further assessment, treatment targets, monitoring, collaboration, level of care, and follow-up.
Differential diagnosis
Compare explanations—do not collect labels
A useful differential is prioritized and evidence based. It distinguishes the leading explanation from reasonable alternatives and urgent conditions that must be excluded.
Does the symptom cluster, duration, course, and impairment fit?
Could another psychiatric condition explain the same findings more coherently?
Could illness, pain, neurologic change, pregnancy, endocrine or metabolic factors, or another physiologic process contribute?
Could prescribed medication, nonprescribed substances, intoxication, withdrawal, caffeine, supplements, or interactions contribute?
Could trauma, grief, culture, development, sleep, environment, or an understandable response to circumstances better explain part of the presentation?
What history, collateral, examination, scale, laboratory study, record, or observation would meaningfully change the ranking?
Clinical formulation
Use the 5 Ps to organize—not replace—clinical synthesis
The 5 Ps are prompts for integration. The final formulation should read as a connected explanation, not five disconnected inventories.
Presenting
What is happening now?Current symptoms, pattern, severity, impairment, safety, patient priorities, and the reason help is being sought now.
Predisposing
What increased vulnerability?Genetics, development, temperament, medical conditions, early adversity, attachment, learning history, chronic stress, and structural inequities.
Precipitating
What changed or triggered this episode?Loss, conflict, trauma, transition, illness, medication change, substance exposure, sleep disruption, hormonal change, or another recent stressor.
Perpetuating
What is keeping the problem going?Avoidance, disrupted routines, ongoing stress, substance use, medication effects, untreated illness, isolation, reinforcement patterns, or barriers to care.
Protective
What supports recovery and safety?Strengths, insight, skills, values, relationships, culture, community, housing, treatment engagement, resources, and reasons for living.
Synthesis test
A strong formulation answers “so what?”
It explains why the leading impression is most coherent, what remains uncertain, which interacting factors are clinically important, what strengths can be mobilized, and why the proposed next steps fit this patient.
- Uses patient-specific evidence rather than generic disorder facts
- Integrates biological, psychological, social, cultural, and developmental factors
- Includes strengths and protective factors—not only deficits
- Identifies modifiable contributors and treatment targets
- Shows how uncertainty will be addressed safely
- Directly informs the plan, monitoring, and level of care
Patient has depression and anxiety with insomnia, family history, school stress, cannabis use, and limited support. Rule out ADHD, bipolar disorder, PTSD, and substance-induced disorder.
The current presentation is most consistent with a depressive episode with prominent anxiety and insomnia, emerging during escalating academic and relationship stress. Family mood history and prior episodes may increase vulnerability, while irregular sleep, high caffeine exposure, intermittent cannabis use, and avoidance of coursework appear to intensify and maintain current symptoms. Brief periods of late-night productivity lack the sustained mood, energy, and behavioral change currently needed to support hypomania, although longitudinal clarification remains important before treatment decisions that could increase activation risk. Engagement in care, future goals, and a trusted support are meaningful strengths. Initial care should address safety, sleep and substance contributors, diagnostic clarification, and the patient's most impairing symptoms while monitoring mood pattern over time.
Common reasoning errors
Know what weakens the formulation
Reasoning becomes less reliable when the clinician anchors early, treats screening results as diagnoses, overlooks medical or substance contributors, confuses trauma exposure with a trauma disorder, or interprets culturally shaped behavior through an unexamined norm.
- Copying the symptom list into a paragraph without synthesis
- Assigning multiple diagnoses to explain every symptom
- Using “rule out” without identifying the missing or conflicting evidence
- Ignoring chronology, baseline, functional change, and context
- Forcing data to fit the first hypothesis
- Creating a plan that is not connected to the stated formulation
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Whole-person reasoning
Keep psychiatric and medical explanations in the same frame
Formulation should connect mental health with physical health, medications, substances, sleep, reproductive and developmental factors, nutrition, pain, cognition, access to care, relationships, and social conditions. Integrated reasoning avoids the false choice between “psychiatric” and “medical” when both may be clinically relevant.