Dementia Screening Accuracy is Robust to Premorbid IQ Variation: Evidence from the Addenbrooke's Cognitive Examination-III and the Test of Premorbid Function

Background: Scores on cognitive screening tools for dementia are associated with premorbid IQ. It has been suggested that screening scores should be adjusted accordingly. However, no study has examined whether premorbid IQ variation affects screening accuracy. Objective: To investigate whether the screening accuracy of a widely used cognitive screening tool for dementia, the Addenbrooke's cognitive examination-III (ACE-III), is improved by adjusting for premorbid IQ. Methods: 171 UK based adults (96 memory service attendees diagnosed with dementia and 75 healthy volunteers over the age of 65 without subjective memory impairments) completed the ACE-III and the Test of Premorbid Function (TOPF). The difference in screening performance between the ACE-III alone and the ACE-III adjusted for TOPF was assessed against a reference standard; the presence or absence of a diagnosis of dementia (Alzheimer's disease, vascular dementia, or others). Results: Logistic regression and receiver operating curve analyses indicated that the ACE-III has excellent screening accuracy (93 sensitivity, 94 specificity) in distinguishing those with and without a dementia diagnosis. Although ACE-III scores were associated with TOPF scores, TOPF scores may be affected by having dementia and screening accuracy was not improved by accounting for premorbid IQ, age, or years of education. Conclusion: ACE-III screening accuracy is high and screening performance is robust to variation in premorbid IQ, age, and years of education. Adjustment of ACE-III cut-offs for premorbid IQ is not recommended in clinical practice. The analytic strategy used here may be useful to assess the impact of premorbid IQ on other screening tools.