Assessing the diagnostic accuracy (DA) of the Spanish version of the informant-based AD8 questionnaire

Introduction: The AD8 is a brief informant-based questionnaire that may also be self-administered, and which aids in identifying cognitive impairment (CI). Our goal is to assess the diagnostic accuracy (DA) of a Spanish version of that questionnaire.

Material and methods: Cross-sectional study of a clinical sample of patient/informant dyads including 330 subjects with suspected CI or dementia (DEM) and 71 controls. We evaluated internal consistency (Cronbach's alpha) and validity (partial correlations with GDS stage, Fototest results and functional index measure [FIM]). We assessed DA for CI vs no CI (GDS stage 3-4) using the area under the ROC curve (AUC), and the cut-off with the highest Youden index was determined to be optimal.

Results: In the sample, 105 subjects had no CI, 99 had CI without DEM and 203 had DEM. Internal consistency was high (α 0.90, 95% confidence interval: 0.89-0.92), as were correlations with the GDS score (r=0.72, P<.001), Fototest results (r=-0.61, P<.001) and FIM (r=0.59, P<.001). The AUC for AD8 was 0.90 (95% confidence interval: 0.86-0.93), which was not significantly different from that of the Fototest (AUC 0.93, 95% confidence interval: 0.89-0.96). The optimal cut-off point was 3/4 with a sensitivity of 0.93 (95% confidence interval: 0.88-0.96) and a specificity of 0.81 (95% confidence interval: 0.72-0.88); 88.8% of the classifications were correct. Combined use of AD8 and the Fototest significantly improved the DA of both (AUC 0.96, 95% confidence interval: 0.93-0.98, P<.05).

Conclusions: The Spanish version of the AD8 questionnaire preserves the psychometric qualities and DA of the original. Using this test in combination with the Fototest significantly increases the DA of both tests.