Objective To report the diagnostic utility of Codex (cognitive disorders examination), a two–step decision tree (Belmin et al. 2007) using three–word recall and spatial orientation from the MMSE and a simplified clock drawing test, for the detection of dementia and mild cognitive impairment.

Methods/Setting Prospective observational study, Cognitive Function Clinic.

Results Of 162 patients tested (M:F=83:79; age range 20–89 years, median 61 years) over a 9–month period (February–November 2012), 43 had dementia by DSM–IV–TR criteria and 29 had MCI. Codex diagnostic categories (A–D) and MMSE scores were highly negatively correlated (n=57; r=–0.68). Taking Codex categories C and D as indicators of dementia, Codex was found to have good sensitivity and specificity for the diagnosis of dementia (0.84 and 0.82 respectively). Taking these categories as indicators of cognitive impairment (dementia and MCI), Codex sensitivity and specificity were 0.68 and 0.91 respectively. Area under the ROC curve, a measure of diagnostic accuracy, was 0.85 for diagnosis of both dementia and cognitive impairment.

Conclusions In this pragmatic study, Codex had good sensitivity and specificity for diagnosis of dementia. However, extending its scope to MCI diagnosis showed poor sensitivity although specificity remained high.