Compare baseline and 6-month follow-up plasma and cerebrospinal fluid (CSF) levels of amyloid β peptides 1–40 (Aβ1–40) and 1–42 (Aβ1–42), total tau protein (T-tau) and phosphorylated tau at threonine 231 (P-tau231) in patients with Alzheimer's disease (AD) and vascular dementia (VD).

21 patients with AD and 7 patients with VD based on the criteria of Diagnostic Statistical Manual 4th edition were assessed at baseline and 7 with AD and 6 with VD were re-assessed 6 months later. Assessments included the Mini-Mental State Exam (MMSE), the Global Deteriorate Scale (GDS), plasma and CSF levels of Aβ1–40 and Aβ1–42, and CSF levels of T-tau and P-tau231 (using a sandwich enzyme-linked immunosorbent assay).

At baseline there were significant differences between AD and VD patients in the mean CSF levels of T-tau (t=2.580, P=0.016), P-tau231 (t=4.014, P=0.000) and Aβ1–40 (t=2.766, P=0.010). At baseline in AD patients, duration of illness was negatively correlated with CSF P-tau231 levels (r=-0.485, P=0.026), MMSE scores (r=-0.565, P=0.008) and GDS scores (r=-0.482, P=0.027); and CSF Aβ1–42 levels were positively correlated to MMSE scores (r=0.565, P=0.008) and negatively correlated with GDS scores (r=-0.634, P=0.002). In the AD patients plasma Aβ1–40 levels increased significantly over the 6-month follow-up period (t=-2.735, P=0.041).

Plasma Aβ1–40 levels increased significantly in AD patients after 6-months of follow-up, that means levels of plasma Aβ1–40 could imply the development of Alzheimer disease. Moreover, CSF P-tau231 and CSF Aβ1–42 levels are associated with the severity of dementia and cognitive impairment.