Capacity vs competence is one of those ethics topics that looks “soft” until it shows up as a hard USMLE question: a refusing patient, a family member yelling, an intoxicated trauma victim, or a delirious older adult with an urgent surgical need. If you can quickly separate capacity (clinical, decision-specific) from competence (legal, global), you’ll unlock a ton of Step-style vignettes.
Why USMLE Cares: The Core Distinction
Capacity (Clinical)
Capacity is a clinical determination made by a physician (or clinical team) about whether a patient can make a specific medical decision at a specific time.
- Decision-specific: A patient might have capacity to consent to a blood draw but not to refuse high-risk surgery.
- Time-specific: Capacity can fluctuate (e.g., delirium, intoxication, hypoglycemia).
Competence (Legal)
Competence is a legal determination made by a judge/court about whether a person has the overall legal ability to make decisions.
- Global label in the eyes of the law (though real-world legal nuance exists)
- Clinicians do not declare someone “incompetent” on exams—use “lacks capacity” instead.
High-yield phrasing (use this on Step):
- Say “The patient lacks decision-making capacity”, not “incompetent.”
- Competence → court. Capacity → clinician.
Quick Table: Capacity vs Competence
| Feature | Capacity | Competence |
|---|---|---|
| Who determines it? | Physician/clinician | Judge/court |
| Scope | Decision-specific | Global legal status |
| Can it change over time? | Yes (often fluctuates) | Usually more fixed, requires legal process to change |
| Context | Medical consent/refusal | Contracts, legal decisions, guardianship |
| USMLE language | “Lacks capacity” | “Declared incompetent by a court” |
The “Pathophysiology” Angle (What Actually Impairs Capacity?)
Capacity isn’t a brain region—it’s a function. USMLE will test conditions that transiently or chronically disrupt cognition, reality testing, or executive function.
Common Step Triggers That Reduce Capacity
- Delirium (infection, medications, withdrawal, metabolic derangements)
- Intoxication (alcohol, sedatives, opioids; also withdrawal)
- Psychosis (fixed delusions affecting the decision)
- Severe depression (esp. hopelessness/psychomotor retardation impacting reasoning)
- Dementia (variable—mild dementia may still allow capacity)
- Acute medical issues: hypoxia, hypoglycemia, uremia, hepatic encephalopathy
- Pain, fear, shock (can impair attention/understanding)
High-yield nuance: A psychiatric diagnosis does not automatically remove capacity. The key is whether it prevents the patient from meeting the capacity criteria for the decision at hand.
What Capacity Looks Like Clinically (Vignette Patterns)
Patients who often have capacity
- Calm patient with schizophrenia who can explain risks/benefits and give a consistent choice—even if you disagree with their values.
- Older adult with mild dementia who can understand the proposed treatment and paraphrase consequences.
Patients who often lack capacity (classic Step setups)
- Delirious hospitalized patient pulling lines, fluctuating attention, disoriented.
- Intoxicated patient refusing life-saving imaging or surgery.
- Manic patient making impulsive, inconsistent decisions with poor appreciation of risk.
- Psychotic patient refusing antibiotics because “the pills are government trackers” (delusion drives decision).
How to Assess Capacity: The 4-Part Test (Must Know)
On exams, capacity is essentially whether the patient can:
- Communicate a choice
- Understand relevant information (diagnosis, options, risks/benefits)
- Appreciate the situation and consequences (apply info to self)
- Reason about options (compare choices logically)
If any are missing → lacks capacity for that decision right now.
Easy way to “test” capacity in a vignette
Ask the patient to:
- Explain their condition in their own words
- Describe what could happen if they accept vs refuse
- Explain why they prefer one option
- Maintain a consistent choice over the interview
High-yield: Patients can make “bad” decisions and still have capacity. Capacity is about the process, not whether you like the outcome.
Diagnosis (Step-Style): What Do You Do Next?
When a patient refuses care
- Assess capacity
- If capacity present → respect refusal (autonomy), document informed refusal
- If capacity absent → treat under emergency doctrine or seek surrogate/guardian depending on urgency
When it’s not an emergency
- If patient lacks capacity, you generally:
- Identify a surrogate decision-maker (healthcare proxy, durable power of attorney)
- Use substituted judgment (what patient would want)
- If unknown, use best interest standard
When it is an emergency
If delaying would cause serious harm or death, you can treat without consent under implied consent (emergency exception), especially when no surrogate is immediately available.
Treatment/Management: What “Fixes” Capacity?
Capacity can be reversible. Management often means treating the underlying condition and optimizing the decision environment.
Practical steps (high yield)
- Treat reversible causes: oxygen, glucose, naloxone if appropriate, manage infection, correct electrolytes
- Reduce iatrogenic contributors: anticholinergics, benzos (if worsening delirium)
- Provide interpreter if needed (language barrier ≠ lack of capacity)
- Control pain and anxiety
- Ensure hearing aids/glasses; quiet room; reorient
- Reassess later if non-urgent
Key exam point: If capacity is impaired due to a reversible condition and the situation is not emergent, stabilize first, then reassess.
Consent Basics You’ll See Alongside Capacity
Informed consent requires:
- Capacity
- Disclosure (risks/benefits/alternatives)
- Understanding
- Voluntariness (no coercion)
Exceptions to consent
- Emergency (implied consent)
- Therapeutic privilege is rarely the right answer on USMLE and ethically controversial—be cautious.
High-Yield Associations & Classic USMLE Traps
1) “Family wants treatment but patient refuses”
- If patient has capacity, the patient decides—even if family disagrees.
- If patient lacks capacity, the surrogate decides (but still aim for the patient’s known wishes).
2) “Intoxicated patient refusing life-saving care”
- Often lacks capacity due to intoxication → treat if emergent.
- If unclear, the safest next step is formal capacity assessment; in emergencies you don’t delay life-saving care.
3) “Psych patient refusing treatment”
- Don’t assume incapacity.
- Determine whether decision is driven by delusion/hallucination impairing understanding/appreciation/reasoning.
4) “Depressed patient refusing dialysis/chemo”
- Severe depression can impair appreciation (“nothing matters,” hopelessness).
- Evaluate capacity, treat depression, reassess if possible.
5) “Patient is confused but agrees to everything”
- Agreeing automatically doesn’t prove capacity. They still must understand and reason.
6) Capacity is decision-specific
- A patient can lack capacity to refuse a high-risk procedure but still have capacity for low-risk choices.
Mini Algorithm (Memorize This)
Patient refuses recommended care
- Assess capacity (4-part test)
- If has capacity → respect refusal + document informed refusal
- If lacks capacity:
- Emergency? Yes → treat (implied consent)
- Not emergency → surrogate decision-maker → substituted judgment → best interest
Documentation: What USMLE Wants You to Say You Did
When capacity is questioned, document:
- Patient’s mental status (orientation/attention)
- The 4 elements (choice, understanding, appreciation, reasoning)
- Information disclosed (risks/benefits/alternatives)
- Interpreter use if relevant
- Who the surrogate is if needed
- Rationale for emergency treatment if applicable
First Aid Cross-References (Where This Lives)
In First Aid (Behavioral Science / Ethics), this topic typically appears under:
- Informed consent
- Decision-making capacity
- Surrogate decision-making
- Emergency exception (implied consent)
Because First Aid editions vary in exact layout/year, use the index for:
- “Capacity”
- “Competence”
- “Informed consent”
- “Implied consent”
- “Surrogate decision maker”
Rapid-Fire Review (Exam-Style One-Liners)
- Capacity = clinical, physician, decision-specific, can fluctuate.
- Competence = legal, court, broad legal status.
- Capacity requires: choice, understanding, appreciation, reasoning.
- Bad decision ≠ no capacity.
- Psych diagnosis ≠ automatic incapacity.
- Emergency + no capacity + no surrogate → treat under implied consent.
- If not emergent: treat reversible cause, reassess, use surrogate if still lacking capacity.