Two-stage capacity test
What it means
Assessing capacity has two stages. STAGE 1 (diagnostic): is there an impairment of, or disturbance in, the functioning of the mind or brain? STAGE 2 (functional): because of that, is the person UNABLE to do ANY ONE of — UNDERSTAND the information, RETAIN it (long enough to decide), WEIGH it in the balance, or COMMUNICATE the decision? Failing any one = lacks capacity for THAT decision.
Worked example
A delirious patient can understand and retain but cannot WEIGH the information against his fluctuating beliefs — he fails the 'weigh' limb, so lacks capacity for this decision, despite being able to talk about it.
In the exam
To decide whether an acutely confused inpatient can consent, the doctor first checks for a brain/mind disturbance, then whether he can understand, retain, weigh and communicate the specific decision.
What settles it
Capacity is DECISION-specific and TIME-specific — a person may have capacity for one decision but not another, and capacity can fluctuate (reassess).
Classically confused with
Mental Capacity Act — 5 principles
Source: MCA 2005; GMC