Determining whether someone has mental capacity to make a decision: clinical guidance based on a review of the evidence.

Valid consent to healthcare treatments depends upon a person having the capacity to give it. The Mental Health Act not only requires a presumption of capacity but also expects clinicians to take reasonable steps to establish whether the patient lacks capacity. The facts are that (1) lack of capacity is common among hospital inpatients and people in the community needing care, but is often not recognized. (2) Capacity must not be judged on the basis of the decision made: an unwise decision is not evidence of a lack of capacity, and a decision expected by the clinician is not evidence of capacity. Capacity is decision-specific and must be considered critically without preconceptions. There is no valid other test. (3) Clinically people will fall into four groups: (a) obviously lack capacity and will not recover it, (b) obviously lack capacity but will recover soon, (c) obviously have capacity, (d) capacity is in doubt and major healthcare decision needed. Only the last group need more detailed attention. (4) Capacity is (a) relative to the complexity of the information; (b) on a spectrum, not categorical; (c) decided using clinical judgement; and (d) subject to disagreement among assessors. The recommendations are as follows: (1) capacity should always be considered within the decision-making process, and the outcome should be documented, with sufficient information to understand the opinion given. (2) Detailed assessment should be reserved for situations when (a) a major decision is needed and (b) there is time to assess and discuss the assessment.