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Assessing capacity

Possible stations 

  • Schizophrenic requires surgery for appendicitis but refuses
  • A patient decides to stop all active treatment for metastatic cancer
  • A patient wants to self-discharge against medical advice

The rules

  • The patient has capacity until proven otherwise
  • Capacity is decision-dependent (i.e. a patient may lack capacity to make one decision but have capacity to make another)
  • If a patient lacks capacity, you must act in their best interests
  • If a patient makes a strange or irrational decision, this does not mean they don’t have capacity

Two-stage test to assess capacity

The patient only lacks capacity if the answer to both questions is YES:

Does the patient have impairment/disturbance of brain function? 

  • If NO, then the patient has capacity (and you do not need to move on to step 2)

If YES, does this mean they are unable to make a decision as a result?

To assess ability to make a decision, you must determine if the patient can:

  • Understand information relevant to the decision (e.g. consequences, risks, benefits, alternatives)
  • Retain the information (for long enough to make a decision)
  • Weigh up/use the information to make a decision (pros and cons)
  • Communicate the decision (by any means)

If the patient can still do all of these, then the patient has capacity.

Best interests

If a patient over 18 years old lacks capacity, it is the doctor’s duty to make the decision on their behalf, acting in their best interests under the Mental Capacity ActThe relatives/friends have no legal right to make the decision unless they have power of attorney (for health and welfare). To decide upon the patient’s best interests, you must:

  • Try to involve the patient in the decision
  • Take into account any of their known beliefs/views
  • Consult anyone identified by patient/carers to help determine what is in their best interests (but not make the decision)
  • Check for any lasting power of attorney (for health and welfare) – must be seen; if in place, you must follow their wishes
  • Consider if they may regain capacity

NB: if a life-changing decision needs to be made for a patient who lacks capacity and does not have relatives who can be involved, an opinion from an independent mental capacity advocate (IMCA) should be requested.

Forms and documentation

  • You must clearly document all parts of your capacity assessment, stating why the patient does not have capacity for the decision
  • If you are stopping or would stop a patient without capacity from doing things they may want to (e.g. leaving hospital) and they are under continuous supervision/control, you are ‘depriving them of their liberties’ and must fill in a Deprivation of Liberty Safeguards (DoLS) form

Mental Health Act

Allows detention of a patient with a mental health disorder who is at risk of harm to themselves or others (nothing to do with capacity)


  • Certain sections allow treatment* as well as assessment but you can treat only their mental illness without their consent
    • However, this can be cautiously extended to treat problems causing or caused by the mental disorder, e.g. overdose
    • If a physical illness is unrelated to the mental disorder, this can only forcibly be treated under the mental capacity act

Sections of the Mental Health Act

Section 2*28 days for assessment and treatment (by 2 doctors but one must be MHA approved)
Section 3*6 months for treatment (by 2 doctors but one must be MHA approved)
Section 472 hours for emergency assessment (by 1 doctor, and an approved mental health practitioner, or the patient’s closest relative)
Section 5(2)72 hours detainment for assessment of patient already in hospital (by doctor in charge of patient’s care)
Section 5(4)6 hours detainment for assessment of patient already in hospital (by approved mental health nurse)

NB: common law may be used in emergencies when there is no opportunity to determine a patient’s mental capacity or mental state. It may be used for detention if the patient is at risk to themselves or others; and/or for the minimum treatment of any illness if urgent intervention is required to save the patient’s life or to prevent a significant deterioration in their condition. It is used most frequently in the emergency department.

Here are some scenarios to test your understanding

You are called to a patient on the medical unit admitted with a paracetamol overdose. They have a history of depression and have been assessed as high risk. They are trying to leave and the nurse asks you what to do?

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A patient who is currently sectioned under section 3 in a mental health unit with schizophrenia, develops an acute limb ischaemia. They are presented with the risks of death without amputation. They decline the operation. What would you do?

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A patient who has encephalitis needs treatment with IV aciclovir. They remove their cannula and refuse for another one to be reinserted. They are unable to understand the risks of not having the treatment. What do you do? What if they repeatedly pull it out?

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An 82 year old female is brought to the emergency department after ingesting organophosphate. She will not survive without treatment. She does not have a history of a mental health disorder. She understands, retains, weighs up and communicates the decision to not have treatment. She does not seem depressed. She explains she has nothing to live for anymore as her husband died 5 years ago, she has no friends and wants to die. What do you do?

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