Screening for dementia in an Irish community sample using MMSE: a comparison of norm-adjusted versus fixed cut-points

Abstract

Background: The MMSE is a widely-used instrument in screening for dementia in the community. The traditional cut-point of <24/30 may be unsuitable for use in some settings, due to biases in age and education.

Objectives: This study aimed to investigate whether cut-points derived from age- and education-specific norms would improve the performance of the MMSE as a screening tool for dementia and cognitive impairment in an Irish community setting, potentially reducing the number of onward referrals. A secondary aim was to obtain score norms in an Irish sample.

Methods: One thousand one hundred and fifteen people aged over 65 (mean age 74.8+/-6.8 years; 68% female) were assessed in their own homes, using MMSE (world) and the AGECAT computerised diagnostic system for mental illness in the elderly. The performance of the MMSE in identifying case- and sub-case-level dementia was investigated using cut-points of <24 and <23, as well as adjusted cut-points based on published norms and norms derived from the Irish sample.

Results: Published norms did not prove useful in improving screening accuracy. Cut-points based on 10th percentile Irish norms and the <23 cut-point performed comparably well, both yielding 93% specificity, with overall accuracy of 90% and 91% respectively (as sensitivity was higher for the <23 cut-point).

Conclusions: Locally-derived norms yielded better screening accuracy than did published norms or the traditional <24 cut-point. The importance of selecting an appropriate percentile cut-off when using norms is discussed. The best results were obtained with a simple <23 cut-point, and this may be optimal when screening for dementia in an Irish community setting.