Sialic acid associated with oxidative stress and total antioxidant capacity (TAC) expression level as a predictive indicator in moderate to severe Alzheimer's disease

•Alzheimer's disease is one of the most common neurodegenerative disease with multiple risk factors.•We aim to find out the most specific biomarker from the peripheral blood samples of Alzheimer's patients.•Protein carbonyl group and lipid peroxidation were increased in cases as compared to controls.•Sialic acid was increased significantly parallel to the oxidative stress parameters with decreased level of antioxidants.