Background: The Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE) is a widely used screening tool for dementia. We aimed to determine the ability of the German version of the 16-item IQCODE with a two-year time frame to discriminate healthy mature control participants (NC) from mild cognitive impairment (MCI) and probable early Alzheimer's disease (AD) patients (all with Mini-mental State Examination (MMSE) scores ≥ 24/30) and to optimize diagnostic discriminability by shortening the IQCODE.

Methods: 453 NC (49.7% women, age = 69.5 years ± 8.2, education = 12.2 ± 2.9), 172 MCI patients (41.9% women, age = 71.5 years ± 8.8, education = 12.3 ± 3.1) and 208 AD patients (59.1% women, age = 76.0 years ± 6.4, education = 11.4 ± 2.9) participated. Stepwise binary logistic regression analyses (LR) were used to shorten the test. Receiver operating characteristic curves (ROC) determined sensitivities, specificities, and correct classification rates (CCRs) for (a) NC vs. all patients; (b) NC vs. MCI; and (c) NC vs. AD patients.

Results: The mean IQCODE was 3.00 for NC, 3.35 for MCI, and 3.73 for AD. CCRs were 85.5% (NC-patient group), 79.9% (NC-MCI), and 90.7% (NC-AD), respectively. The diagnostic discriminability of the shortened 7-item IQCODE (i.e. items 1, 2, 3, 5, 7, 10, 14) was comparable with the longer version (i.e. 7-item CCRs: NC-patient group: 85.3%; NC-MCI: 80.1%, NC-AD: 90.5%).

Conclusions: The German 16-item IQCODE with two-year time frame showed excellent screening properties for MCI and early AD patients. An abbreviated 7-item version demonstrated equally high diagnostic discriminability, thus allowing for more economical screening.

Background: Dementia screening in elderly people with low education can be difficult to implement. For these subjects, informant reports using the long (L) (26 items) and short (C) (16 items) versions of the Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE) can be useful. The objective of the present study was to investigate the performance of Brazilian versions of the IQCODE L, S and a new short version (SBr) (15 items) in comparison with the Mini-mental State Examination (MMSE) for dementia screening in elderly people with low education.

Methods: Thirty-four patients with mild to moderate dementia, diagnosed according to ICD-10 criteria, and 57 controls were evaluated and divided into three groups based on their socioeconomic status and level of education. Patients were evaluated using the MMSE and the informants were interviewed using the IQCODE by interviewers blind to the clinical diagnosis.

Results: Education was correlated with MMSE results (r = 0.280, p = 0.031), but not with the versions of the IQCODE. The performance of the instruments, evaluated by the ROC curves, was very similar, with good internal consistency (Cronbach's α = 0.97). MMSE correctly classified 85.7% of the subjects while the three IQCODE versions (L, S and SBr) correctly classified 91.2% of the subjects.

Conclusions: The long, short and the new short Brazilian IQCODE versions can be useful as a screening tool for mild and moderate patients with dementia in Brazil. The IQCODE is not biased by schooling, and it seems to be an adequate instrument for samples with low levels of education.