Assessing capacity is part and parcel of being a doctor. A patient's ability to make a decision with regard to treatment is central to the interaction between doctor and patient, and affects the care you provide.

What is capacity?

Capacity is the ability to make a decision or take an action that impacts on a person's life; it indicates that a person is able to make a decision with regard to their own care and treatment.

A clinician caring for a person who may lack capacity to consent or decline a treatment or proposed course of action needs to assess the patient's capacity in the first instance.

The Mental Capacity Act

The assessment of capacity is set out in the Mental Capacity Act (MCA) 2005 and its accompanying Code of Practice. This provides a framework for those caring for or treating people aged 16 or over in England and Wales, to guide the provision of support for people who temporarily or permanently lack the ability to make decisions for themselves. The MCA requires the clinician to assess a patient's capacity before carrying out any care or treatment.

In Scotland, the Adults With Incapacity Act (Scotland) 2000 covers decision-making concerning mental capacity in adults.

The assessment of capacity is time- and decision-specific. This means that you should assess a patient's capacity to make a specific decision at the time the decision needs to be made. You should not decide that someone lacks capacity based solely on reference to their age, appearance, condition or behaviour. Bear in mind also that the inability to make a major or more complex decision does not mean that a person is unable to make a smaller or simpler decision.

The MCA embodies five key principles. The first three help the health professional to determine whether a patient lacks capacity. Only if you determine that capacity is lacking do the final two principles come into play to support the process of decision making.

Principle 1 – the presumption of capacity

This principle dictates that capacity should be assumed unless proven otherwise. So you cannot assume that someone is unable to make a decision for themselves based solely on their having a particular medical condition or disability; you should assume that a person has capacity to make the decision in question, unless it is demonstrated otherwise.

Principle 2 – support the individual

A patient should be provided all practicable help before they are deemed unable to make their own decisions. You should make every effort to support a patient in making a specific decision for themselves if possible. This might include providing support through an advocate, a translator, or a speech and language therapist to help with other forms of communication. Even if a lack of capacity is established, you should still involve the patient as far as possible in making the relevant decision.

Principle 3 – unwise decision

Remember that a patient has the right to make a decision that you might disagree with or consider irrational or unwise. This does not indicate a lack of capacity, but may reflect individual preferences or values. The ability to make the decision is key; not the decision itself.

Principle 4 – best interests

Any decision made or action taken for or on behalf of a person who lacks mental capacity must be done in their best interests. 'Best interests' is not defined by the MCA or the Code of Practice, and depends on individual circumstances, which are taken to include a person's welfare, social, emotional and psychological interests as well as their medical interests.

Regard must be taken of the patient's current or previously expressed wishes or desires and their beliefs and values, though these feelings are not, in and of themselves, decisive.

Principle 5 – least restrictive option

A health professional making a decision on behalf of a person lacking capacity must consider whether it is possible to delay making the decision until the person regains capacity; or, if a decision is required, to make a decision that interferes less with the person's rights or freedoms.

If a person is temporarily incapacitated and the decision can be deferred until they regain capacity, this should be done. If not, the decision made must be in the person's best interests, bearing in mind that where possible the least restrictive option must be considered.

Decision making

The determination as to whether someone has the capacity to make a particular decision involves a two-stage test:

Stage 1:  Whether there is an impairment of or disturbance in the functioning of the patient's mind or brain, temporary or permanent. If so, then:

Stage 2:  Is the impairment or disturbance sufficient that the person is unable to make a particular decision at the time it needs to be made?

The MCA states that someone is unable to make a decision if they cannot do one or more of the following:

• Understand the information relevant to the decision (including the reasonably foreseeable consequences of whatever decision is made or of failing to make a decision).
• Retain that information in making the decision.
• Use or weigh the information available, and
• Communicate the decision by any means, including speech, sign language, or simple muscle movement.

A person failing any one or more aspects of this test is deemed to lack the relevant capacity. However, you must try to find ways of communicating with a patient before determining that they lack capacity. You may need to consider the views of those close to the patient, including family, friends, carers or other professionals – though the decision as to whether a patient has or lacks capacity is for you to make.

You should record why there is uncertainty as to the patient's capacity, as well as details of your assessment and conclusions. The record should make clear how any decision about the patient's best interests was reached, the reasons for the decision, who was consulted, and what factors were considered.

Only when a patient has been determined to lack the capacity to make a particular decision should a decision be made for or on behalf of that person. Any such decision should be made in the best interests of the patient.

The MCA provides further guidance on the factors that a decision-maker acting on behalf of a patient should consider in deciding what is in a person's best interests.