HLA Crossmatch Tests
Once compatible blood type is established, a HLA (Human Leukocyte Antigen) crossmatch is completed.
What is HLA?
HLA are protein molecules that are located on the surface of almost all cells in the body. They play a role in recognizing cells that are your own (self) from those that are foreign (non-self). Nearly 600 different HLA molecules have been identified. Through a blood test, the laboratory determines which HLA markers are present. HLA markers are inherited. There are six HLA markers that are looked at for transplantation purposes. We inherit three from our mother, and three from our father. When you hear about "matching" this is what is being looked at.
The most likely way to find a match between two people is among siblings.
- There is a 25% chance that siblings will inherit the same genes from their parents. This would be considered a "perfect match."
- There is a 50% chance that siblings will be a "half match" to a sibling, and
- There is a 25% chance that siblings will not share any HLA markers in common.
With advances in immunosuppressive medication, transplants can still take place and be successful even if there are no HLA markers in common. We know that the "perfect match" works better and lasts longer. For this reason, we do HLA typing along with a crossmatch on all siblings who come forward to donate to determine who would be the best potential candidate. Otherwise, a crossmatch is completed prior to medical clearance and HLA typing is completed prior to the actual transplant surgery.
Some people develop HLA antibodies that can attack what is identified as foreign. It is important to perform a crossmatch to determine if the recipient has developed antibodies against any of the donor HLA markers. Antibodies are formed due to exposure to things that the body recognizes as foreign. People who have had previous transplants, pregnancies, blood transfusions or infections may develop antibodies that make it more difficult to match them with other people. It is important to perform a crossmatch to determine compatibility.
What is a crossmatch?
The crossmatch is thought to be a miniature test transplant performed in the laboratory. To complete this test a sample of blood is taken from the donor and recipient. The blood must be drawn at the same time. In the laboratory, the donor blood cells are mixed with the recipient serum.
Only those with a negative crossmatch can proceed with the donor evaluation. A negative reaction means that the recipient does not have antibodies against the donor HLA and a transplant can be performed. If the recipient serum kills off the donor cells, this is a positive crossmatch and a transplant would not survive.