Diagnostic utility of the Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE) and its combination with the Addenbrooke's Cognitive Examination-Revised (ACE-R) in a memory clinic-based population

Objective: The study aimed to assess the clinical utility of the Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE) in patients referred to memory clinics, alone and in combination with the Addenbrooke's Cognitive Examination-Revised (ACE-R) and the Mini-mental State Examination (MMSE). Methods: This pragmatic prospective study was based on consecutive referrals attending with an informant (n = 144) to two memory clinics over a 12-month period. Patients were diagnosed using standard clinical diagnostic criteria for dementia (DSM-IV) as gold standard (dementia prevalence = 59%). The IQCODE was administered to informants, and the ACE-R and/or MMSE to most patients. Results: The IQCODE proved acceptable to informants, and was quick and easy to use. Using traditional parameters of diagnostic utility (sensitivity, specificity, positive predictive value, likelihood ratios), the performance of the IQCODE at optimal test accuracy was highly sensitive (0.86) for the diagnosis of dementia but specificity was poor (0.39) with suboptimal positive predictive value (0.67) and small or unimportant likelihood ratios. Overall diagnostic accuracy based on area under the receiver operating characteristic (ROC) curve was 0.71. Combining the IQCODE with either ACE-R or MMSE greatly improved accuracy, specificity and positive predictive value when the tests were used in series, but not when used in parallel. Conclusion: In a memory clinic based population, the IQCODE proved sensitive for the diagnosis of dementia but overall diagnostic accuracy was suboptimal. Combining the IQCODE in series with the ACE-R or MMSE greatly improved diagnostic utility.