Medical decision-making competence

This week’s Lancet contains a study by Raymont et al investigating the prevalence of mental incapacity in medical inpatients and associated risk factors (see also this item in Shrinkette’s blog ).

In order to judge medical decision-making competence, the authors used two tools: the MacArthur competence assessment tool for treatment (MacCAT-T), and clinical vignettes (based on something called the “Thinking Rationally About Treatment” research method).

After excluding 143 patients for severe cognitive impairment, altered level of consciousness and refusal to participate, 159 patients were interviewed. Of these, 50 (31%) were deemed lacking in capacity to make medical decisions.

Lack of capacity was correlated with increasing age and with a poor score on the Mini Mental Status Exam. The median MMSE score was 29 (out of a maximum of 30) in patients with capacity and 22 in those without capacity.

Significantly, when the clinical team caring for the patients and close relatives were asked to judge the patients’ capacity, those with capacity were correctly assessed almost 100% of the time, but those deemed lacking in capacity by the authors were judged incompetent only 25% of the time by the physicians and similarly by the relatives.

The conclusion to the abstract: “Mental incapacity is common in acutely ill medical inpatients, and clinicians tend not to recognise it. Screening methods for cognitive impairment could be useful in detecting those with doubtful capacity to consent”.
Are we really underestimating patients’ decision-making capacity as badly as this article suggests? Possibly, but I have a few reservations about the study.

The MacCAT-T tool used to assess medical decision-making capacity is a relatively new one. How valid is it? If three-quarters of physicians caring for the patients and three quarters of their relatives judged the patients who “failed” the MacCAT-T assessment to be competent, it makes me wonder as much about the validity of the tool as about the physicians’ and relatives’ assessments.

According to the authors:

MacCAT-T is a semi-structured interview that measures: (1) understanding of the disorder and its treatment, including associated benefits and risks; (2) appreciation of the disorder and its treatment–ie, how the patient understands they could be specifically affected, which usually entails some level of insight; (3) reasoning, which assesses the processes behind the decision and ability to compare alternatives in view of their consequences; and (4) the ability to express a choice.

I am no expert in such assessment tools, but it seems to me that this sort of assessment might bias, for example, against people who have crackpot medical ideas. Are they necessarily incompetent?

Since the assessment of medical competence correlated well with the MMSE assessment in this study, wouldn’t we be better off relying on the MMSE itself, which is not limited to medical decision making capacity? The determination of a patient’s specific competence to make medical decisions seems somehow more paternalistic and prone to bias than a more general assessment of mental status.

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