Decision-making capacity and surrogate decisions

Capacity evaluation follows a structured four‑component model:

1. Understanding – the patient must grasp the nature of the condition, the proposed intervention, and the likely benefits and risks.
2. Retention – the patient should be able to hold this information long enough to use it in deliberation.
3. Weighing (appreciation and reasoning) – the patient must consider how the information relates to personal values and circumstances, comparing alternatives.
4. Communicating a choice – the patient must express a decision, verbally or by any reliable method.

These components are derived from the core elements identified in capacity evaluations for dementia and other conditions. The clinician first assesses each ability and then makes a judgment of overall capacity for the particular decision, taking into account the context and the risk–benefit ratio. ^[4]

• Explain the decision in plain language, checking for comprehension after each key point.
• Ask the patient to repeat the information in their own words (tests understanding and retention).
• Explore values by asking how the options align with the patient’s goals (weighing).
• Confirm the choice using a clear, unambiguous response (communication).

If any element is deficient, the patient is deemed to lack capacity for that decision and a surrogate may be consulted.

Capacity is not a static trait; it lies on a continuum ranging from adequate to marginal to inadequate. Conditions such as delirium, medication side‑effects, or fluctuating dementia can cause capacity to vary over time. In such cases: ^[4]

• Re‑assessment should be scheduled when the patient’s mental state stabilises.
• Supported (or assisted) decision‑making can be employed, whereby the clinician or a designated supporter helps the patient maximise residual capacity while preserving autonomy.
• Advance directives or a Lasting Power of Attorney allow patients to appoint a trusted individual to make decisions on their behalf when capacity is lost.

When a patient lacks the capacity to decide about their own treatment, the law requires another person to act on their behalf. In England and Wales this role is set out in the Mental Capacity Act 2005, which adopts a person‑centred, flexible best interests (substituted interests) approach. The surrogate may be a person named in a Lasting Power of Attorney, a court‑appointed Deputy, or, failing those, the responsible clinician. ^[3]

Surrogates can be guided by several theoretical standards (Phillips & Wendler identify five)^[1]:

The substituted judgement standard is often described as the “what would the patient have wanted?” approach. It requires the surrogate to infer the patient’s preferences from prior statements, values, and known wishes. In practice, clinicians gather this information through discussions with family, friends, and any advance care planning documents^[1]; the aim is to approximate the patient’s own decision‑making process rather than to impose the surrogate’s own values. ^[3]

A key practical step is the best interests meeting. The clinician retains ultimate responsibility for the clinical judgment, while the surrogate contributes contextual knowledge. ^[1]

If the patient’s prior wishes are unknown or ambiguous, the surrogate must fall back on the best interests test. This test is deliberately broad, allowing consideration of medical, emotional, social, and spiritual factors^[1]. However, critics argue that the test is “opaque” and places unfair demands on parents or families who must balance the patient’s needs with their own. To mitigate this, some commentators propose a harm threshold: only intervene when a decision would cause ^[3]

The best interests standard is the cornerstone of surrogate decision‑making for patients lacking capacity. It requires the decision‑maker to consider all relevant factors and to weigh them in a way that promotes the overall welfare of the patient^[1]. The MCA frames this as a substituted interests approach, meaning that the surrogate should aim to achieve what would be in the patient’s best interests, not merely what the surrogate thinks is best^[1]. ^[3]

Because “best interests” can be indeterminate, many scholars suggest that a harm threshold should mediate the test. In this view, the first question is whether the proposed decision would cause harm to the patient. If it would, the surrogate must intervene to prevent that harm; if not, the decision can be left to the surrogate’s discretion within the broader best‑interests framework. The courts use harm to narrowly focus upon (defective) parental care, allowing a clearer evaluative term th ^[1]

Mrs L, a 78‑year‑old with advanced dementia, has no advance directive. Her daughter believes her mother would not want aggressive ventilation. The clinical team explains that ventilation could prolong life but would likely cause distress. No clear prior wish is documented. The team assesses that withholding ventilation would not cause significant harm and proceeds with a best‑interests discussion, ultimately deciding not to intubate.

Because best‑interests decisions can incorporate a range of values, transparency is essential. Making explicit which values are influencing the decision (e.g., prioritising the patient’s dignity over prolonging life) allows families to understand the reasoning and provides a basis for lawful challenge if they disagree. This openness also respects the principle that the child’s (or adult’s) interests should not be automatically subordinate to parental or family interests, a point highlighted by bioethicists who critique the traditional best‑interests test.

• Surrogates act under the MCA, using either substituted judgement (what the patient would have wanted) or, when that is unavailable, the best‑interests test.
• The best‑interests test is broad and value‑laden; critics note its indeterminacy.
• A harm threshold can serve as an initial filter, providing a clearer line for when surrogate decisions may be overridden.
• Effective decision‑making requires systematic information gathering, transparent weighting of values, and collaborative discussion with families, while clinicians retain ultimate clinical responsibility.

In England and Wales the law recognises that children develop the ability to understand and weigh information about their health as they grow. A child under 16 is presumed not to have the capacity to consent to treatment, but the presumption is rebuttable if the child demonstrates sufficient understanding of the specific decision – the so‑called “Gillick competence”. When a child is judged competent, the clinician must obtain informed consent from the child directly; otherwise a parent or legal guardian provides proxy consent. If a competent child refuses treatment, the clinician must respect that refusal unless the treatment is life‑saving, in which case the court may be approached for a best‑interest order. ^[4]

For adolescents aged 16–17 the statutory presumption is that they have capacity, but they may still be asked to involve a parent if the clinician thinks support would aid understanding. In emergency situations where delay would cause significant harm, treatment may proceed without consent under the doctrine of implied consent, but documentation of the decision‑making process remains essential.

• Capacity is decision‑specific and time‑specific.
• “Gillick competence” allows a child under 16 to consent if they understand the nature, purpose and risks of the proposed treatment.
• Where capacity is lacking, parental or guardian consent is required; the child’s wishes should still be sought and respected where possible.
• In life‑threatening emergencies, treatment may be given without consent, but the rationale must be recorded.

The Mental Capacity Act (MCA) 2005 provides the statutory framework for assessing and supporting decision‑making capacity in England and Wales. Its five statutory principles are: ^[3]

1. Presumption of capacity – every adult is assumed to have capacity unless proven otherwise.
2. Support to enable decision‑making – clinicians must take reasonable steps to help a person understand information.
3. Unwise decisions are not evidence of incapacity – a person may make a choice that others consider irrational and still retain capacity.
4. Best‑interest decisions – when a person lacks capacity, any act or decision must be made in their best interests, considering past wishes and values.
5. Least restrictive option – interventions should interfere as little as possible with the person’s freedom.

These principles intersect with psychiatric practice, particularly when assessing fluctuating capacity. Although the term is not statutory, it appears in the MCA Code of Practice and case law to describe capacity changes that accompany episodes of mental illness such as mania in bipolar disorder. A typical course shows capacity deteriorating during an acute episode and recovering as symptoms remit. Clinicians must therefore reassess capacity repeatedly, rather than assuming a permanent loss. ^[2]

Formal capacity testing is not required for every patient. In clear cases—e.g., severe dementia where the patient cannot understand the nature of a decision—capacity can be inferred. However, when the situation is ambiguous, when family members disagree, or when a judicial review is anticipated, a structured assessment is advisable. The Mini‑Mental State Examination (MMSE) is often used as a screening tool; scores below 16 strongly correlate with impaired capacity, whereas scores > 24 correlate with retained ability. ^[4]

• Over‑reliance on a single test – Using only the MMSE can miss subtle deficits; a comprehensive assessment is required.
• Failing to document the process – The MCA mandates clear records of how the person’s wishes, values and best‑interest considerations were weighed; poor documentation can lead to legal challenges.
• Ignoring the “least restrictive” principle – Interventions that are more restrictive than necessary breach the MCA and may constitute unlawful interference.
• Misapplying surrogate hierarchy – When proxy consent is needed, the accepted order is spouse, adult child, parents, siblings, then lawful guardian; deviating from this without justification can be contested. ^[4]
• Treating “unwise” decisions as incapacity – A patient may refuse a recommended treatment for personal reasons; this does not automatically mean they lack capacity.

The MCA underpins everyday clinical interactions—from obtaining consent for a simple blood test to deciding on major surgical procedures. In elective surgery, clinicians must confirm that the patient understands the risks, benefits and alternatives; if capacity is lacking, a surrogate decision‑maker follows the hierarchy outlined in the surrogate consent guidance.

In mental health services, the Act guides the use of sectioning under the Mental Health Act. Although the MCA does not appear in the Mental Health Act (1983), its principles influence how clinicians assess whether a patient can consent to voluntary admission. When a patient’s capacity fluctuates, as in bipolar mania, repeated assessments are required to determine whether compulsory treatment is justified. ^[2]

In research, proxy consent is required when participants lack capacity. The process must respect the participant’s previously expressed wishes and be documented meticulously. Failure to adhere to the MCA can expose clinicians to claims of assault, battery or civil trespass, as the Act was originally enacted to protect staff from such legal actions when treating incapacitated patients. ^[3]