Establishment of the test method of the Aβ42 in the serum of the alzheimer disease patient and its clinical significance

Objective To establish a enzyme-linked immunosorbent assay (ELISA) method for detecting the β-amyloid peptide 42（Aβ42） and explore its clinical meaning for diagnosis and treatment in the early stages of the alzheimer disease (AD). Methods Using the Aβ42 single chain variable fragment constructed by phage antibody library display system as coat antibody, associated with the Aβ42 polyclonal antibody acquired by Aβ42 immunized rabbit and HRP labeled goat anti rabbit IgG to establish ELISA method for detecting the Aβ42 in peripheral blood.The method was used it to test the Aβ42 in 120 vascular dementia（VD） or cerebral vessel infarction patients and 120 AD patients and 120 controls.The methodology performance were evaluated. Results The inter and intra coefficient of variable (CV) of this self-established ELISA method was 3.6% and 3.5%, 6.8% and 7.1% respectively.The recovery rate was 97.2%-103.1%.The linear range was 0.050-2 μg/L. Its reactivity decreased <12% when it was put in both 37 ℃ for 6 days and 4 ℃ for 6 months.Compared with the Belgium INNOTEST reagent by testing 90 samples simultaneously, the results of self-established method was (0.207±0.039) μg/L, the results of INNOTEST was (0.206±0.038) μg/L; the regression equation was Y=1.011X-0.003, R2=0.979, P<0.01. The Aβ42 in blood of AD group was (0.247±0.032) μg/L, VD or cerebral vessel infarction group was (0.173±0.028) μg/L, control group was (0.172±0.032) μg/L. The Aβ42 in AD group was higher than that in the VD or cerebral vessel infarction group and control group (q=18.867, 18.907 respectively, P<0.01).The cut off value was 0.212 μg/L decided by the receiver operating characteristic (ROC) curve.The reference interval was 0-0.212 μg/L.The sensitivity of this ELISA method was 86.7% (104/120) and specificity was 90.8% (218/240). Conclusions The ELISA method for detecting Aβ42 in peripheral blood established by the study is sensitive and specific and has good precision and stability.It could provide a new effective criterion and support for the early diagnosis and treatment of the AD patients.（Chin J Lab Med, 2012, 35:42-46） Key words: Alzheimer disease; Amyloid beta-protein; Peptide fragments; Enzyme-linked immunosorbent assay