Some people donate blood stem cells on more than one occasion, either to the same patient or to different ones. If you have blood stem cells removed, new ones will be generated to replace them, in much the same way as your blood is replaced when you make a blood donation. So it is possible to donate more than once. However, to minimize the strain on donors as far as possible, we try to keep those that have made a donation as backups, just in case their patient has a relapse and more blood stem cells are needed. We also use our Replacement Donor Program to prevent multiple donations. This identifies donors with identical combinations of tissue characteristics so we have a backup for each one.