Validity and diagnostic accuracy of the Auditory Consonant Trigram (ACT) Test in Turkish patients with mild cognitive impairment and Alzheimer’s disease

Purpose: This study is a multi-method validity study aimed to evaluate the clinical usefulness of the Auditory Consonant Trigram (ACT) Test in distinguishing healthy controls, patients with Mild Cognitive Impairment (MCI), and patients with Alzheimer's disease (AD). Materials and Methods: A total of 166 participants aged 50–86 years were included: 22 with AD, 20 with MCI, and 124 healthy controls. All participants first completed a battery of standardized neuropsychological tests, followed by the ACT Test. Results: Significant group differences were found in ACT Test scores, indicating an impairment gradient across delay intervals (Control > MCI > AD). ACT Test total scores correlated moderately to strongly with general cognitive functions, memory, and executive functions. Logistic regression analysis found that ACT Test significantly distinguished patients with AD from controls (OR = 0.89, %95 CI [0.84–0.96]), but did not differentiate patients with MCI from controls (OR = 1.04, %95 CI [0.91–1.19]). In the extended model that included age and other cognitive variables, ACT Test was not an independent predictor. ROC analysis showed strong discrimination for AD (AUC = 0.89, 95% CI [0.83–0.94]) with a cut-off point of ≤ 39, sensitivity of 91% (95% CI [0.71–0.99]), and specificity of 82% (95% CI [0.74–0.89]). Adjusting for age further improved accuracy in the age-adjusted model. Conclusion: The ACT Test provides robust discrimination of AD and shows meaningful convergent associations with multiple cognitive domains.