Context: Evaluation of the capacity of a patient to make medical decisions should occur in the context of specific medical decisions when incapacity is considered.
Objective: To determine the prevalence of incapacity and assessment accuracy in adult medicine patients without severe mental illnesses.
Data sources: MEDLINE and EMBASE (from their inception through April 2011) and bibliographies of retrieved articles.
Study selection: We included high-quality prospective studies (n = 43) of instruments that evaluated medical decision-making capacity for treatment decisions.
Data extraction: Two authors independently appraised study quality, extracted relevant data, and resolved disagreements by consensus.
Data synthesis: Incapacity was uncommon in healthy elderly control participants (2.8%; 95% confidence interval [CI], 1.7%-3.9%) compared with medicine inpatients (26%; 95% CI, 18%-35%). Clinicians accurately diagnosed incapacity (positive likelihood ratio [LR+] of 7.9; 95% CI, 2.7-13), although they recognized it in only 42% (95% CI, 30%-53%) of affected patients. Although not designed to assess incapacity, Mini-Mental State Examination (MMSE) scores less than 20 increased the likelihood of incapacity (LR, 6.3; 95% CI, 3.7-11), scores of 20 to 24 had no effect (LR, 0.87; 95% CI, 0.53-1.2), and scores greater than 24 significantly lowered the likelihood of incapacity (LR, 0.14; 95% CI, 0.06-0.34). Of 9 instruments compared with a gold standard, only 3 are easily performed and have useful test characteristics: the Aid to Capacity Evaluation (ACE) (LR+, 8.5; 95% CI, 3.9-19; negative LR [LR-], 0.21; 95% CI, 0.11-0.41), the Hopkins Competency Assessment Test (LR+, 54; 95% CI, 3.5-846; LR-, 0; 95% CI, 0.0-0.52), and the Understanding Treatment Disclosure (LR+, 6.0; 95% CI, 2.1-17; LR-, 0.16; 95% CI, 0.06-0.41). The ACE was validated in the largest study; it is freely available online and includes a training module.
Conclusions: Incapacity is common and often not recognized. The MMSE is useful only at extreme scores. The ACE is the best available instrument to assist physicians in making assessments of medical decision-making capacity.