 The investigators will utilize the institutions current population of 8 eligible chronically exchanged transfused participants at the T.C. Thompson Childrens Infusion Clinic. The eligible participants will be invited to participate in a cross over design study so that each participant serves as its own control. Eight participants will be randomly assigned blinded envelope whereby four participants will start with rapid manual partial exchange transfusion: 3 months will be spent in a wash out period, then 3 months of data collection for RMPET. This group will then be switched to simple transfusion with a wash out period of three months, then data collection for three months. The second group of four participants will start with simple transfusion and have an identical study design over 12 months 3 months of collected data during simple transfusion, a 3 month wash out period, switch to rapid manual partial exchange transfusion for three months, then 3 months of data collection for RMPET. 