Only about 1% of regis­tered donors actual­ly dona­te stem cells after typ­ing. Fol­low-up tests
are per­for­med in rough­ly a third of all poten­ti­al donors. The fro­zen blood sam­ple from typing
can usual­ly be used for this pur­po­se. Addi­tio­nal tests may some­ti­mes fol­low, mea­ning that
new blood sam­ples will be needed.