Informant Accuracy of IQCODE, AD8 and GPCOGi for diagnosis of dementia: Does your friend know best?

Abstract

Background Increasing numbers of people are requiring evaluation for possible dementia. There has been limited research exploring the accuracy of informant questionnaires in primary care. Methods A diagnostic accuracy study to explore the influence of informant relationship type on the accuracy of IQCODE, AD8 and GPCOGi in primary care. 240 participants were recruited from 21 general practitioner (GP) surgeries in the South West of England. The reference standard for a diagnosis of dementia was made against ICD-10 criteria based on specialist clinician assessment. A threshold of greater than 3.3 on IQCODE, greater or equal to 2 on AD8 and less than 5 on the informant component of GPCOG (GPCOGi) was used to indicate an abnormal test. Results Of 238 participants with informant data, 131 had dementia, 60 CIND, and 47 had normal cognition. Median informant age was 70 years (IQR 60 years to 78 years). 71% of informants were female and 56% of informants were spouses. On all three questionnaires, compared to spouses, adult descendants tended to score participants more cognitively impaired, whereas friends scored participants less cognitively impaired. However, there was little evidence of difference by informant relationship type once fully adjusted. Overall accuracy was similar for all three informant questionnaires with an AUROC of 0.67 (95% CI, 0.62 to 0.72) for IQCODE, 0.64 (95% CI, 0.60 to 0.69) for AD8 and 0.59 (95% CI, 0.56 to 0.63) for GPCOGi. Friends tended to have the highest AUROC at 0.89 (95% CI 0.78 to 1) for IQCODE, 0.88 (95% CI 0.77 to 0.99) for AD8 and 0.69 (95% CI 0.57 to 0.81) for GPCOGi. This difference was significant for IQCODE (p=0.0004) and AD8 (p=0.0001). Conclusions Most informants were either a spouse or adult descendant. Overall, informants, when using IQCODE, AD8 or GPCOGi may be useful at ruling out dementia but less useful for ruling it in. We found no evidence of difference between spouse or adult descendants but friends (while accounting for only 8% of informants) performed significantly better overall on IQCODE and AD8 due to an increase in specificity without loss of sensitivity.