At the UMHS Histocompatibility Laboratory potential recipients are typed for HLA-A, B, C, DRB1,3,4,5, DQB1, loci by high resolution (allele level) molecular methods. The methods utilized for HLA typing are SSOP, SSP and/or SBT. In addition to the HLA high resolution typing patients are screened for preformed anti-HLA antibodies, the detection of anti-HLA antibodies directed to possible mismatches in less ideal donors is related with delay in the platelets and neutrophil engraftment and even with graft rejection. The HCT donor could be family member known as related donor or an unrelated donor. RELATED DONOR: Half of the HLA alleles or haplotype are inherited from the mother and half from the father, so each recipient’s sibling who has the same parents has a 25% chance of matching. There is less chances to find a matched donor in the extended family members, however, in cases where the recipient carry a rare allele or haplotype in combination with a frequent haplotype is recommended extend the searching to relatives such as grandparents, aunts, uncles or cousins. Related donor donors are initially screened by low resolution techniques for HLA-A,B and DRB1. For those 6/6 or 5/6 matched donors a high resolution confirmatory typing for HLA-A, B, C, DRB1,3,4,5, DQB1will be performed. High-resolution typing results are reported to transplant physicians for final selection. UNRELATED DONOR: About 70% of patients who need a transplant do not have a suitable related donor. For these patients the high resolution typing for HLA-A, B, C, DRB1,3,4,5, DQB1 a searching request is submitted to the National Marrow Donor Program (NMDP) and other registries around the world, to find a matched unrelated donor among the nearly 18.5 million voluntary donors and more than 590,000 cord blood units. When an unrelated matched donor is identified a sample is shipped to our laboratory for a confirmatory high resolution typing. Possible donors high-resolution typing results are reported to transplant physicians for final selection.