Evaluation of Plasma Amyloid Peptides Aβ(1-40) and Aβ(1-42) as Diagnostic Biomarker of Alzheimer's Disease, its Association with Different Grades of Clinical Severity and 18F-Fluorodeoxyglucose Positron Emission Tomography Z score in the Indian Population: A Case-Control Study

BACKGROUND: We estimated plasma amyloid-peptides levels (Aβ(1-42) and Aβ(1-40)) as diagnostic biomarker of Alzheimer's disease (AD) and evaluated its association with clinical severity and 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET) Z score of the different brain regions in the Indian population. PATIENTS AND METHODS: A case-control study was conducted. Diagnostic and statistical manual-IV, Dubois, and NIA-AA criteria were used for the diagnosis of AD. The plasma Aβ(1-42) and Aβ(1-40) concentration and 18F-FDG PET Z score were estimated for different brain regions. RESULTS: Forty-seven cognitive impairment patients (AD = 29, mild cognitive impairment = 18) and 33 age-matched controls were enrolled. Plasma Aβ(1-42) level was significantly higher in the AD group compared to controls (P = 0.046) and a cut-off >5.7 ng/mL has a specificity of 96.9%, sensitivity of 27.6%, positive predictive value 88.9%, and negative predictive value 60.4% for differentiating AD patients from controls. Significant correlation was seen between Aβ(1-40)/Aβ(1-42) ratio and 18F-FDG PET Z score in the bilateral-parietal, temporal, frontal-association area, and posterior-cingulate areas. CONCLUSION: As a diagnostic biomarker of AD, plasma Aβ(1-42) level showed good specificity but low sensitivity in the Indian population.