Assessment of patient capacity to consent to treatment

Edward Etchells, Peteris Darzins, Michel Silberfeld, Peter A. Singer, Julia McKenny, Gary Naglie, Mark Katz, Guyatt Gordon H, D. William Molloy, David Strang

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OBJECTIVE: To compare results of a specific capacity assessment administered by the treating clinician, and a Standardized Mini-Mental Status Examination (SMMSE), with the results of expert assessments of patient capacity to consent to treatment. DESIGN: Cross-sectional study with independent comparison to expert capacity assessments. SETTING: Inpatient medical wards at an academic secondary and tertiary referral hospital. PARTICIPANTS: One hundred consecutive inpatients facing a decision about a major medical treatment or an invasive medical procedure. Participants either were refusing treatment, or were accepting treatment but were not clearly capable according to the treating clinician. MEASUREMENTS AND MAIN RESULTS: The treating clinician (medical resident or student) conducted a specific capacity assessment on each participant, using a decisional aid called the Aid to Capacity Evaluation. A specific capacity assessment is a semistructured evaluation of the participant's ability to understand relevant information and appreciate reasonably foreseeable consequences with regard to the specific treatment decision. Participants also received a SMMSE administered by a research nurse. Participants then had two independent expert assessments of capacity. If the two expert assessments disagreed, then an independent adjudication panel resolved the disagreement after reviewing videotapes of both expert assessments. Using the two expert assessments and the adjudication panel as the reference standard, we calculated areas under the receiver-operating characteristic curves and likelihood ratios. The areas under the receiver-operating characteristic curves were 0.90 for specific capacity assessment by treating clinician and 0.93 for SMMSE score (2p = .48). For the treating clinician's specific capacity assessment, likelihood ratios for detecting incapacity were as follows: definitely incapable, 20 (95% confidence interval [CI] 3.6, 120); probably incapable, 6.1 (95% CI 2.6, 15); probably capable, 0.39 (95% CI 0.18, 0.81); and definitely capable, 0.05 (95% CI 0.01, 0.29). For the SMMSE, a score of 0 to 16 had a likelihood ratio of 15 (95% CI 5.3, 44), a score of 17 to 23 had a likelihood ratio of 0.68 (95% CI 0.35, 1.2), and a score of 24 to 30 had a likelihood ratio of 0.05 (95% CI 0.01, 0.26). CONCLUSIONS: Specific capacity assessments by the treating clinician and SMMSE scores agree closely with results of expert assessments of capacity. Clinicians can use these practical, flexible, and evaluated measures as the initial step in the assessment of patient capacity to consent to treatment.

Original languageEnglish
Pages (from-to)27-34
Number of pages8
JournalJournal of General Internal Medicine
Issue number1
Publication statusPublished - 6 Feb 1999
Externally publishedYes


  • Informed consent
  • Mental competency
  • Reliability of results

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