VWF MM ratio before, during and after acute iTTP episodes. VWF MM ratios in patients with iTTP from 2 days to 28 weeks (median 39 days) before an acute bout (n = 14), at the onset of the acute iTTP episode (n = 16), after first TPE (n = 20), and in remission after the acute episode (n = 20). Gray background is the normal range of the VWF MM ratio assessed in controls.