Background: Verbal fluency (VF) tasks are simple and efficient clinical tools to detect executive dysfunction and lexico-semantic impairment. VF tasks are widely used in patients with suspected dementia, but their accuracy for detection of mild cognitive impairment (MCI) is still under investigation. Schooling in particular may influence the subject's performance. The aim of this study was to compare the accuracy of two semantic categories (animals and fruits) in discriminating controls, MCI patients and Alzheimer's disease (AD) patients.

Methods: 178 subjects, comprising 70 controls (CG), 70 MCI patients and 38 AD patients, were tested on two semantic VF tasks. The sample was divided into two schooling groups: those with 4–8 years of education, and those with 9 or more years.

Results: Both VF tasks – animal fluency (VFa) and fruits fluency (VFf) – adequately discriminated CG from AD in the total sample (AUC = 0.88 ± 0.03, p < 0.0001) and in both education groups, and high educated MCI from AD (VFa: AUC = 0.82 ± 0.05, p < 0.0001; VFf: AUC = 0.85 ± 0.05, p < 0.0001). Both tasks were moderately accurate in discriminating CG from MCI (VFa: AUC = 0.68 ± 0.04, p < 0.0001; VFf: AUC = 0.73 ± 0.04, p < 0.0001) regardless of the schooling level, and MCI from AD in the total sample (VFa: AUC = 0.74 ± 0.05, p < 0.0001; VFf: AUC = 0.76 ± 0.05, p < 0.0001). Neither of the two tasks differentiated low educated MCI from AD. In the total sample, fruits fluency best discriminated CG from MCI and MCI from AD; a combination of the two improved the discrimination between CG and AD.

Conclusions: Both categories were similar in discriminating CG from AD; the combination of both categories improved the accuracy for this distinction. Both tasks were less accurate in discriminating CG from MCI, and MCI from AD.