Alzheimer's Disease vs Control: Aβ42 (Plasma and Serum)


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Meta-analysis of of more than 50 studies did not show a convincing difference between Alzheimer’s disease patients and controls: The effect size was quite small (1.049) and the p value was only marginally significant (0.03). However, while the level of Aβ42 in blood is not by itself a good biomarker for AD, the Aβ42:Aβ40 ratio has gained attention as a plasma biomarker that predicts amyloid-PET status regardless of clinical diagnosis (Doecke et al., 2020; Pérez-Grijalba et al., 2019).

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How to interpret a forest plot: Each individual effect size (ES) is a ratio of the mean biomarker level in one condition over the mean level in another condition. An ES equal to 1 means that the two conditions had identical mean values. An ES > 1 indicates higher levels in the first condition, whereas an ES < 1 indicates lower levels in the first condition. The overall ES, indicated by a black diamond, is a weighted average of the individual effect sizes. The weight of each data point was determined by the inverse of the variance and is reflected in the size of each square. The width of the overall ES diamond is determined by the 95 percent confidence interval. Data out of range of the scale, including ES and confidence intervals, are indicated by an arrowhead at the edge of the plot, when applicable. 

Version 3.0, July 2021.