Limits on the use of the MMSE for assessment of capacity to consent for treatment

This study explores to what extent patients scoring in the normal Mini-Mental Status Examination (MMSE) cognitive range have mental incapacity to consent to treatment; and analyzes the relationship between MMSE score and MacArthur Competence Assessment Tool for Treatment (MacCAT-T) scores. Eighty medical inpatients, 40 psychiatric inpatients and 40 healthy controls were assessed. The criterion of expert psychiatrists was the 'gold standard' for capacity. Seven (63.6%) psychiatric patients and two (14.3%) medical patients without capacity performed in a normal MMSE cognitive range (p < 0.001). Statistically significant correlations between MMSE scores and mean MacCAT-T scores were observed in both patient groups (particularly in 'understanding' and 'reasoning'). The MMSE should not be used on its own for assessment of capacity.