Hello Susan. The article you referenced is correct when selecting a donor for STEM CELL transplantation to replace a diseased bone marrow. The easiest pool to find a match from is siblings because they share the same parents. However, irradiation can't be used in Stem Cell transplants to prevent GVH disease because it would prevent the stem cells from being able to replicate themselves in their new bone marrow home, which is the purpose of stem cell transplants for blood cancers like Lymphoma. This is different than transfusions of RBCs, which are used to replace blood lost in surgery, trauma or during chemotherapy. Parents may be a match for ABORh blood types with their children, but may be a big mismatch for other antigens displayed on White Blood cells (immune system cells) which are still present at low levels in Red Blood cell products. So the difference is the type of cellular blood product being used (RBCs vs Stem cells), how closely the donor needs to be matched to the antigens present on the recipient's cell and whether GVH disease can be mitigated by irradiation. Hope this helps. Please feel free to ask further questions if this isn't clear from my explanation. And I'm sure I included TMI, but I enjoy sharing my nerdiness with others. Thanks!