Fig. 2

The levels of plasma tau and ptau181 in healthy people detected by the Simoa method. Meta-analysis of studies calculating plasma tau levels (a) and plasma ptau181 levels (b) of different age groups in the healthy population. In ptau181 studies, the average age in Rodriguez et al. was considerably higher; the control cohort used in Suarez-Calvet et al. comprised ‘middle-aged’ adults; the TRIAD cohort in Karikari et al. included young individuals; all of which may have contributed to the heterogeneity