Mental Capacity Assessment – OSCE Guide

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Mental capacity refers to the ability of an individual to use and understand informationΒ to make a decision, and then to communicate the decision made.1

Doctors are often asked to assess whether someone’s decision-making is impaired by illness so that we can ensure decisions are made in the patient’s best interests.

As part of an OSCE station, you may be required to assess mental capacity or discuss with an examiner how you would approach capacity assessment in a specific scenario. This guide provides a step-by-step approach to assessing the capacity of an adult patient in an OSCE setting.

Defining capacity

Patients may lack capacity due to an impairment of the brain or mind. This may be a progressive impairment (e.g. dementia), a permanent injury (e.g. traumatic brain injury), or a temporary impairment (e.g. delirium, intoxication).2

As mental state can fluctuate, capacity must be reassessed at regular intervals.

Capacity should always be discussed in decision-specific terms. For example, while an individual may not understand the risks and benefits of having a blood test, they may still be able to decide what to wear or eat. This empowers patients and upholds their dignity.

You should assume capacity unless proven otherwise. You should never assume that an individual lacks capacity because of their medical or psychiatric history, appearance, behaviour or beliefs.Β 

Individuals are entitled to make decisions that you consider unwise, or different to the decision that you would make if they have the capacity to make this decision.

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Preparing for the capacity assessment

Before conducting a capacity assessment, review the patient’s medical notes to understand their functional status, recent illness progression, and any previous capacity assessments. If able, discuss with the wider multidisciplinary team (e.g. nursing colleagues) any concerns they may have.

Beforehand, consider whether you are the most appropriate person to conduct the capacity assessment. If the capacity assessment relates to a specific procedure, it should be one you have a good understanding of.

Consider when to conduct the assessment. Avoid times when confusion or drowsiness are more likely, such as after a nap or following the administration of sedating medications.

Consider who should be present for the assessment. The patient may feel more comfortable with familiar staff or family present. The family should be informed of the purpose of the assessment and should avoid influencing the patient’s answers.

Opening the consultation

Wash your handsΒ andΒ don PPEΒ if appropriate.

Introduce yourself to the patient including yourΒ nameΒ andΒ role.

Confirm the patient’sΒ nameΒ andΒ date of birth.

Explain the purpose of the conversation: β€œI’d like to chat about making decisions about your care, so we can best support you. Is now a good time?”

Ensure privacy during the assessment so that you will not be disturbed.

Conducting the capacity assessment

To have the capacity to make a specific decision, an individual must demonstrate the following capabilities:

  • Understand information
  • Retain information
  • Use the information to make a decision
  • Communicate their decision

Firstly, the patient must understand the situation and the options presented to them:

  • β€œCould you tell me a bit about why you are in hospital?”
  • β€œDo you understand what the options are for managing your infection?”

Additional support may be required, such as visual or hearing aids, or an interpreter. Be aware that using a family member as an interpreter compromises patient privacy.

Secondly, they must be able to retain this information during the conversation. Do they forget the conversation quickly, or become too distracted to continue? Memory or concentration may be affected by fatigue, sedating medications, or thought disorder. You may need to come back to conduct your assessment another time.

The patient must then show they can weigh up options and make a decision based on their reasoning. This is often a good time to explore patient concerns.

Flawed logic does not mean capacity is lacking, so long as the decision is supported by the patient’s own reasoning.

Lastly, this decision must be communicated back to the assessor. Communication can be verbal, written or indicated with sign language or gestures. Steps should be taken to facilitate communication if required.

Closing the consultation

Thank the patient for their time.

Dispose of PPEΒ appropriately andΒ wash your hands.

Document the outcome of the mental capacity assessmentΒ 


Document your assessment clearly in the medical notes, including:

  • The indication for assessment
  • The decision this relates to
  • Date and time
  • Who was present during the assessment

As capacity can fluctuate, you must make a note of when this decision will next be reviewed. If appropriate, the next of kin should be informed.

Complex cases, or inconclusive assessments, should be discussed with senior clinicians who may recommend specialist assessment by liaison psychiatry.

Legal considerations

If the patient lacks the capacity to make a decision, you should strive to find the least restrictive option (i.e. the option that allows the patient the most freedom).Β 

A supportive legal framework should be implemented to protect their rights, and copies should be made available in the patient’s medical notes. In England and Wales, this documentation is the mental capacity act, overseen by the court of protection.

The deprivation of liberty safeguards (DoLS) should be completed if the decision made infringes on a patient’s ability to leave or if they are controlled or supervised in any way to which they cannot consent to.

In Scotland, different legislation applies (adults with incapacity act).

Any decisions made regarding the patient should be in accordance with their best interests. This can be determined from consulting several sources, including the multidisciplinary team, next of kin and any pre-existing legal documentation that describes their wishes.Β 

The patient may have an advance decision to refuse treatment (ADRT),Β written and witnessed documentation that details specific scenarios in which a patient wishes to refuse specific treatment.

The patient may have appointed a lasting power of attorney for health and welfare (England and Wales) or welfare power of attorney (Scotland). This person, often a family member or friend, is legally appointed by the patient in advance of becoming unwell to make decisions on their behalf if they lack capacity in the future.3,4

Lasting power of attorney for property and finances (England and Wales) or continuing power of attorney (Scotland) cannot make healthcare-related decisions.

Special circumstances

In rare circumstances, it may be necessary to act against the wishes of a capacitous patient if there is an immediate threat to life. A senior clinician must be involved in this situation.

If a patient is detained under the mental health act (MHA), a capacity assessment should still be carried out for all decisions relating to physical health.

The court of protectionΒ is involved in all capacity decisions relating to contraceptive sterilisation, organ donation, and withdrawal of nutrition and hydration during a permanent vegetative state.

Example scenarios

Example 1

Rashida is an 80-year-old woman admitted with a urinary tract infection. She has been refusing to take oral antibiotics, and the nursing team is unclear why this is. She has no past medical history and no signs of delirium. Her interpreter explains that the last time Rashida was prescribed an antibiotic, she experienced severe diarrhoea. She knows this was a different medication but does not want to risk this happening again.

Does this patient have the capacity to refuse antibiotics?

Although this decision may seem irrational, Rashida has demonstrated she understands, retains and has decided upon the information provided and communicates her wishes, which should be respected.

Example 2

John is a 31-year-old man who has presented to the emergency department after taking an overdose of paracetamol with alcohol. When you approach the bedside to gain consent for cannulation, he opens his eyes to voice but is too drowsy to engage in conversation. His wife tells you he has always been afraid of needles. He has no power of attorney and no advance directive.

Does this patient have the capacity to refuse intravenous cannulation?

At present, John does not appear to be able to understand, retain or communicate information due to his intoxication. Although he has a needle phobia, there is no legal documentation in place to suggest he would not want cannulation in this instance. Due to his presentation, it is in his best interests to receive medications and fluids intravenously. This should be discussed with his next of kin, and his capacity reassessed regularly, as his cognition will likely improve over the coming days.


Dr Emma Leighton

Psychiatry Registrar


  1. NHS. Consent to treatment- assessing capacity. Published December 2022. Available from: [LINK]
  2. General Medical Council. Mental capacity Available from: [LINK]
  3. Alzheimer’s Society Legal and financial. Available from: [LINK]
  4. Compassion in Dying. Making decisions and planning your care. Available from: [LINK]


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