Relationship between TPO concentrations in PB and BM. TPO concentrations in NS (•), patients with ITP before (□) and after (▪) treatment, AA (▵), and ET (▴) were measured by ELISA. There was a significant positive correlation between TPO levels in BM and PB in these patients (r = .997). In each subject, the TPO concentrations in BM were consistently higher than those in the PB.