“HLA” is short for Human Leukocyte Antigens, which are proteins in the immune system that determine whether a patient will react against a donor transplant or if the donor transplant cells will react against the recipient. A very good basic tutorial about HLA types is on the Stanford Website, and the national Be The Match program (aka NMDP) has more info on the role of HLA type in transplants of stem cells from bone marrow or cord blood.
The HLA type of cord blood is always assessed by public banks at the time of storing cells, and then the type is listed on a registry that can be searched for patients worldwide who need a transplant. Family/private banks typically do not measure the HLA type at the time of banking, as the actual test specification varies depending on the proposed clinical use and the testing can always be checked later using a testing segment of the stored cells.
In the case of sibling transplantation, individuals have 25 per cent chance of having a sibling who is HLA matched.