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Make the Diagnosis: Medical Decision-Making Capacity

Prior Probability

Decision-making capacity requires the presence of 4 abilities: (1) appreciation of one's situation and the consequence of one's choices, (2) understanding of the information required to make the choice, (3) reasoning about the risks and benefits of choices, and (4) communication of one's choice. While any physician can make this assessment, decision-making capacity must be evaluated in the context of the patient's situation.1

The prevalence of incapacity varies widely with the patient population. The prevalence of incapacity is 2.8% (1.7%-3.9%) in healthy elderly patients; 20% (14%-26%) in those with mild cognitive impairment; 26% (18%-35%) among medical inpatients; and 54% (28%-79%) among those with Alzheimer disease.

Population for Whom Decision-Making Capacity Should Be Considered

The ability of a patient to make decisions is implicitly or explicitly assessed in every patient encounter. Typically, clinicians implicitly use the patient's cognitive abilities as a surrogate marker for decision-making capacity and this will usually work when patients are either cognitively intact or significantly impaired.

When clinicians recognize incapacity, they are frequently correct. However, when incapacity is present, clinicians will detect it in less than half of affected patients. This may be a particular problem in those with mild cognitive impairment. Thus, clinicians must be prepared to do more explicit assessments depending on situational, psychosocial, medical, psychiatric, and neurological factors that can affect the 4 abilities required for medical decision-making capacity.

Assessing the Likelihood of Medical Decision-Making Incapacity

While there is a strong relationship between cognition and capacity, the relationship is not perfect because cognition does not assess all the domains of capacity. However, most studies of capacity instruments also include an assessment of cognitive ability. The Mini-Mental Status Examination (MMSE)2 has been the most frequently studied measure of cognition as a screen for medical incapacity (see Table 84-1).

Table 84-1Useful Findings for Identifying Patients With Medical Decision-Making Incapacity

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