What is HLA Type and how is it used?

The term "HLA" is short for Human Leukocyte Antigens, and these are proteins in the immune system that determine whether a patient will react against a donor transplant.  A very good basic tutorial about HLA types is on the Stanford Website, and the donor registry Be The Match explains the role of HLA Typing and Matching in stem cell transplants on their clinical website.

Briefly, there are 6 HLA types that are important for stem cell transplants: in a bone marrow transplant the patient and donor must match at all 6 (100% match), whereas a cord blood transplant is just as effective at curing patients with only a 4 out of 6 match (67% match) between donor and patient. This is the reason that cord blood donations are so important to help patients who come from minority or mixed racial backgrounds.

The HLA type of cord blood is always measured by public banks, and then the type is listed on a registry that can be searched by patients seeking a transplant.  Family banks typically do not measure the HLA type at the time of banking, because it is an expensive lab test and and can always be checked later from a testing segment of the stored cells.