What is Capacity in Mental Health
Capacity is the functional ability of a person to make a specific decision at a specific time, determined by assessing whether they can understand relevant information, retain it, use or weigh it to make a decision, and communicate their choice. 1
Core Definition and Legal Framework
A person lacks capacity when an impairment or disturbance in the functioning of their mind or brain prevents them from making a specific decision at the time it needs to be made. 1 This impairment can be temporary (such as from intoxication, delirium, or acute illness) or permanent (such as from dementia or brain injury), and the distinction does not affect the assessment process. 1
The law presumes that every adult has capacity until proven otherwise—this is the principle of presumed capacity. 1, 2 You cannot determine lack of capacity based on a patient's age, diagnosis, appearance, behavior, or because they make what appears to be an unwise decision. 1, 2
The Four-Abilities Framework for Assessment
The American College of Physicians recommends assessing capacity by evaluating four core abilities using a structured clinical interview: 2
1. Understanding
The patient must demonstrate ability to understand the basic relevant information about their condition, the proposed intervention, available alternatives, and the risks and benefits of each option including no treatment. 1 This is assessed through direct questioning with open-ended questions. 2, 3
2. Appreciation
The patient must acknowledge their medical condition and appreciate the probable personal consequences of the treatment options—this goes beyond mere understanding to recognizing how the information applies to their own situation. 1, 2
3. Reasoning
The patient must demonstrate ability to weigh the risks and benefits and reach a decision that is logically consistent with that assessment. 1 You evaluate their logical thought processes, not whether you agree with their conclusion. 2
4. Expression of Choice
The patient must be able to clearly communicate a decision indicating their preferred treatment option by any means (verbal, sign language, blinking, hand squeezing). 1
Critical Characteristics of Capacity
Capacity is decision-specific, not global—a patient may have capacity to consent to simple procedures but lack capacity for complex financial or medical decisions. 1, 2 You must specify which decisions the patient can or cannot make rather than making sweeping determinations of incompetence. 2, 4
Capacity is time-specific and can fluctuate, particularly in patients with delirium, dementia, or acute illness. 2, 4 Reassessment is required when the patient's condition changes or when different decisions need to be made. 1, 2
The assessment must be proportionate to the risk of the decision—higher-risk decisions require more stringent demonstration of the four abilities. 2, 4
Common Pitfalls to Avoid
Never rely solely on cognitive screening tests like the Mini-Mental State Examination (MMSE) or Montreal Cognitive Assessment (MoCA) to determine capacity. 2, 4 These tests assess cognitive function but do not evaluate the functional decision-making abilities required for capacity. 2
Do not confuse mental illness with lack of capacity—a person receiving treatment for mental illness, even if detained under mental health legislation, should not be assumed incapable of providing valid consent for medical treatment. 1 The key question is whether they can collaborate with the care team to make the specific decision at hand. 1
An irrational or unwise decision alone does not prove lack of capacity. 1 However, a highly irrational decision based on persistent misinterpretation of information may indicate impaired capacity, though determining incapacity on grounds of irrationality requires legal advice. 1
Documentation Requirements
Document specific examples of how the patient's impairment affects each of the four abilities, your clinical reasoning leading to the determination, and which specific decisions the patient can or cannot make. 2, 4 Include collateral history about baseline function and plans for reassessment when capacity may improve. 2
When Capacity Is Lacking
If you determine a patient lacks capacity, identify the authorized surrogate decision-maker according to local laws (typically spouse, adult child, parent, sibling, or friend in that order). 1, 2 Review any advance directives or previously expressed wishes. 1, 2
Apply substituted judgment when possible—the surrogate should make the decision the patient would have made if capable, based on the patient's known values and preferences. 2 When the patient's wishes cannot be determined, use the best interest standard, making decisions that reflect the patient's beliefs, values, and overall welfare. 1, 2