Figure 1. Plasma tau, diagnosis, and CSF β-amyloid-42 (Aβ₄₂).

Baseline data from the Alzheimer's Disease Neuroimaging Initiative (ADNI). (A) Plasma tau and diagnosis. p Values from a linear regression model with plasma tau as the dependent variable and diagnosis as a categorical predictor, adjusted for APOE ɛ4, age, and sex. Cognitively healthy controls (CNs) had lower levels than patients with Alzheimer disease (AD; β = −0.48, 95% confidence interval [CI] −0.19 to 0.78), and patients with mild cognitive impairment (MCI) had lower levels than patients with AD (β = −0.38, 95% CI −0.65 to 0.098). (B) Plasma tau and CSF Aβ₄₂. The trend line is from a linear regression model with plasma tau as the dependent variable and CSF Aβ₄₂ as the predictor, adjusted for diagnosis, APOE ɛ4, age, and sex. The shaded area indicates the 95% CI. In a sensitivity analysis, we removed the 2 bottom-right observations. This affected the slope, but plasma tau and CSF Aβ₄₂ were still correlated (β = −3.99, 95% CI −7.68 to 0.30, p = 0.034 compared to β = −4.86, 95% CI −8.38 to 1.33, p = 0.0071 with all observations included). The β coefficients are on the original scale of CSF Aβ₄₂; see table 2 for coefficients using standardized data. (C) Plasma tau in diagnostic groups stratified by CSF Aβ₄₂ (Aβ-positive, CSF Aβ₄₂ <192 ng/L, closed circles; Aβ-negative, CSF Aβ₄₂ >192 ng/L, open circles). p Values from a linear regression model testing the effect of the combination of diagnostic group and Aβ status to predict plasma tau, adjusted for APOE ɛ4, age, and sex. Patients with AD had higher plasma tau levels than Aβ-negative CNs (β = 0.62, 95% CI 1.07–0.17), Aβ-positive CNs (β = 0.67, 95% CI 1.16–0.18), Aβ-negative patients with MCI (β = 0.90, 95% CI 1.37 – 0.42), and Aβ-positive patients with MCI (β = 0.43, 95% CI 0.78–0.081), and Aβ-positive patients with MCI had higher plasma tau levels than Aβ-negative patients with MCI (β = 0.47, 95% CI 0.90–0.031).