Capacity is one of the most important legal and ethical concepts in medicine.

It appears frequently in:

UCAT Situational Judgement,
MMI stations,
panel interviews,
ethics discussions,
and NHS hot topics.

Understanding capacity properly helps demonstrate:

ethical reasoning,
patient-centred care,
legal awareness,
professionalism,
and communication skills.

What Is Capacity?

Capacity refers to:

A patient’s ability to make a specific decision about their healthcare.

A patient with capacity can:

understand information,
weigh risks and benefits,
and make their own informed choice.

Key Principle

Adults Are Presumed To Have Capacity

Under UK law:

Every adult is assumed to have capacity unless proven otherwise.

This is extremely important ethically and legally because it protects:

autonomy,
dignity,
independence,
and patient rights.

The Law Behind Capacity

Capacity in the UK is governed by the:

Mental Capacity Act 2005

This law provides:

the legal framework for assessing capacity,
guidance for healthcare professionals,
and rules about best interests and decision-making.

The 5 Core Principles of the Mental Capacity Act

1. Presume Capacity

Every adult has capacity unless proven otherwise.

Doctors should never assume incapacity because:

a patient is elderly,
has a disability,
has mental illness,
or makes an unusual choice.

2. Support Decision-Making

Patients should receive as much support as possible before concluding they lack capacity.

Examples:

simpler language,
interpreters,
visual aids,
involving family,
treating pain first,
improving hearing/vision.

3. People Can Make Unwise Decisions

A strange or risky decision does NOT automatically mean lack of capacity.

Example:
A patient refusing surgery may still fully understand:

the risks,
alternatives,
and consequences.

Doctors assess:

the decision-making process,
NOT whether they agree with the decision.

4. Act in Best Interests

If a patient lacks capacity:

healthcare professionals must act in their best interests.

5. Least Restrictive Option

Interventions should minimise restriction of the patient’s freedom and autonomy.

Capacity Is Decision-Specific

This is one of the most important interview points.

A patient may:

have capacity for one decision,
but lack capacity for another.

Example

An elderly patient with dementia may:

understand a blood test,
but not understand the risks of major surgery.

Therefore:

Capacity must be assessed separately for each decision.

Capacity Can Fluctuate

Capacity is not always permanent.

Patients may temporarily lose capacity due to:

delirium,
intoxication,
infection,
medication,
unconsciousness,
mental illness.

Later, they may regain it.

The 4 Elements of Capacity

A patient must be able to:

1. Understand

Understand relevant information about:

the condition,
treatment,
risks,
benefits,
alternatives.

2. Retain

Retain information long enough to make the decision.

A patient does not need to remember every detail forever.

3. Use or Weigh

Use the information logically to compare:

risks,
benefits,
consequences.

This is often the hardest part.

4. Communicate

Communicate their decision:

verbally,
through writing,
sign language,
gestures,
or communication aids.

Easy Memory Technique

U-R-U-C

Understand
Retain
Use/weigh
Communicate

Very useful in interviews.

The Two-Stage Capacity Test

Capacity assessments often involve:

Stage 1 — Functional Test

Can the patient:

understand,
retain,
use/weigh,
communicate?

Stage 2 — Diagnostic Test

Is there:

an impairment or disturbance affecting the mind or brain?

Examples:

dementia,
delirium,
alcohol intoxication,
psychosis,
brain injury,
unconsciousness.

Important Causes of Impaired Capacity

Temporary Causes

alcohol,
drugs,
delirium,
severe pain,
unconsciousness,
severe infection,
hypoglycaemia.

Long-Term Permanent Causes

dementia,
brain injury,
severe learning disability,
severe mental illness.

Mental Illness ≠ Automatic Lack of Capacity

A patient with:

schizophrenia,
bipolar disorder,
depression,
may still fully have capacity.

Capacity depends on:

the individual decision at that moment.

Capacity vs Consent

Valid Consent Requires:

1. Capacity

The patient can make the decision.

2. Information

The patient understands:

risks,
benefits,
alternatives.

3. Voluntariness

The patient is not pressured or coerced.

Can Patients Refuse Treatment?

Yes — if they have capacity.

Even if:

doctors disagree,
refusal may lead to harm,
refusal may lead to death.

This reflects:

autonomy,
bodily integrity,
legal rights.

Example Scenario

Scenario

A patient refuses life-saving surgery.

Good Answer

You should:

assess capacity carefully,
ensure the patient understands consequences,
communicate empathetically,
explore concerns,
respect refusal if capacity is present.

Best Interests

If a patient lacks capacity:

decisions must be made in their best interests.

What Should Be Considered?

Healthcare professionals should consider:

patient wishes,
values,
beliefs,
previous decisions,
family views,
quality of life,
least restrictive option.

Important Ethical Principle

Best interests does NOT simply mean:

“what doctors want.”

It means:

what most benefits the patient overall.

Advance Decisions

Patients can plan ahead in case they lose capacity later.

Advance Decision to Refuse Treatment (ADRT)

A legally binding refusal of future treatment.

Examples:

refusing CPR,
refusing ventilation,
refusing artificial feeding.

Lasting Power of Attorney (LPA)

A patient can appoint someone to make decisions on their behalf if capacity is lost.

This may involve:

healthcare,
welfare,
living arrangements.

Ethical Principles of Capacity

1. Autonomy

Respecting patient choice.

Capacity assessments protect autonomy by ensuring capable adults make their own decisions.

2. Beneficence

Acting in the patient’s best interests.

3. Non-Maleficence

Preventing harm.

Doctors sometimes intervene when patients lack capacity to avoid serious harm.

4. Justice

Ensuring fair and equal treatment.

Capacity assessments should never discriminate based on:

age,
disability,
appearance,
culture,
mental illness.

Capacity in UCAT Situational Judgement

Capacity often appears indirectly in SJT.

Common themes:

confused patients,
intoxicated patients,
dementia,
informed consent,
refusing treatment,
confidentiality.

Strong answers usually:

prioritise patient safety,
respect autonomy,
involve seniors appropriately,
avoid assumptions,
assess capacity carefully,
communicate respectfully.

Fourteen Questions and Answers

1. What is capacity?

Answer:

Capacity is the ability of a patient to make a specific decision at the time it needs to be made. It is decision-specific and time-specific, meaning a patient may have capacity for one decision but not another.

2. How do you assess capacity?

Answer:

Capacity is assessed using four criteria:
Understand the information relevant to the decision
Retain that information long enough to decide
Weigh up the information as part of decision-making
Communicate their decision
All four must be met for a patient to have capacity.

3. Is capacity a global or specific concept?

Answer:

Capacity is specific, not global. A patient may have capacity to make simple decisions like choosing meals but may lack capacity for complex decisions like surgery consent.

4. What do you do if a patient lacks capacity?

Answer:

If a patient lacks capacity, I would:
Confirm that all efforts have been made to support decision-making
Make a best-interests decision
Involve family or carers where appropriate
Consider any advance decisions or previously expressed wishes
Consult senior colleagues if needed

5. What law governs capacity in the UK?

Answer:

In the UK, capacity is governed by the Mental Capacity Act 2005, which provides a legal framework for assessing capacity and making best-interest decisions when capacity is lacking.

6. What is the presumption of capacity?

Answer:

The presumption of capacity means that every adult is assumed to have capacity unless proven otherwise. This protects patient autonomy and ensures capacity is not unfairly denied.

7. A patient refuses treatment—how do you know if they have capacity?

Answer:

I would assess whether they understand the condition, the treatment, the risks of refusal, and whether they can weigh this information. If they meet all four criteria, they have capacity, even if their decision seems unwise.

8. Can a patient with capacity make an unwise decision?

Answer:

Yes. A patient with capacity has the right to make decisions that others may consider unwise, as long as the decision is informed and voluntary. Capacity is about process, not outcome.

9. What is best interests decision-making?

Answer:

Best interests decision-making is used when a patient lacks capacity. It involves considering clinical benefit, patient values, past wishes, and input from family or carers to decide what would be most beneficial for the patient.

10. What factors might affect capacity?

Answer:

Capacity can be affected by:
Dementia
Delirium
Severe mental illness
Head injury
Intoxication
Severe distress or pain

These may be temporary or reversible.

11. What is the role of family in capacity decisions?

Answer:

Family members provide valuable information about the patient’s wishes and values, but they do not automatically make decisions unless legally appointed as a proxy or Lasting Power of Attorney.

12. What is a Lasting Power of Attorney (LPA)?

Answer:

A Lasting Power of Attorney is someone legally appointed by the patient to make healthcare decisions on their behalf if they lose capacity. They must act in the patient’s best interests and according to known wishes.

13. What is the difference between capacity and consent?

Answer:

Capacity is the ability to make a decision, while consent is the actual agreement to a treatment. A patient must have capacity for consent to be valid.

14. What would you do if capacity is unclear?

Answer:

I would:
Reassess the patient at a different time
Treat reversible causes (e.g., delirium, pain, intoxication)
Involve senior colleagues
Seek a formal capacity assessment if needed

Common Mistakes Candidates Make

1. Assuming Dementia = No Capacity

Incorrect.

Some patients with dementia retain capacity for many decisions.

2. Confusing Bad Decisions With Lack of Capacity

Patients are allowed to make risky or unusual choices.

3. Forgetting Capacity Fluctuates

Patients may regain capacity later.

4. Ignoring Communication Support

Doctors should help patients participate as much as possible.

High-Level Interview Insight

The strongest candidates combine:

legal knowledge,
empathy,
ethics,
and practicality.

Example:

“I would communicate calmly, assess capacity carefully, involve seniors where appropriate, and ensure the patient’s wishes and dignity remain central throughout the decision-making process.”

That sounds mature, safe, and patient-centred.