Discussion Forums > Thalassemia Major
My new born baby has possible Thal major
Sharmin:
Dear Meena,
Your doctor's are confusing genotype matching with HLA matching for a transplant. Genotype matching is genetically determining what type of blood is genetically best matched for you so that cross matching blood for transfusion become easier and more accurate. I am working on posting more information about this procedure - there are certain labs in the US that do the test. For my son, the test was done in Calgary and then sent to Toronto for the testing.
Sharmin
Manal:
Sharmin,i know you explained this million of times but again :huh :huh :-\,
genotyping : is looking in the DNA for your own antigenes in order to know them and therefore choose the suitable blood for these antigens so that no antibodies are formed, right ????????
So in cross matching, what are we looking for?? How does it differ from the phenotyping????
manal
Sharmin:
Hi Manal,
I can understand the confusion surrounding these tests. I also don't know if I am doing a good job describing it therefore I will try to post some links and will probably need some input from Andy.
Cross match - is determining the recipients blood group and Rh. If rbc antibodies are present then the donor blood is tested against the recipient's plasma - if antibodies are present against the donors blood then agglutination will occur and the donor blood will not be a match. This way several donors are tested against the recipients blood until a match is found (when no agglutination occurs).
Phenotype testing - testing of the recipient's red blood cells (remember red blood cells have no nucleus and no dna) to look for markers on the red blood cells. This is best done before a patient has been transfused because once a thal major begins transfusing 2 things prevent phenotype testing 1) the marrow is suppressed and very few retics (hosts own rbcs are produced) 2) donor rbcs are present in the recipient's blood stream. For these reason's the patient's phenotype cannot be accurately determined. If done before transfusions start, the patient's phenotype can be known.
Genotype testing - uses nucleated cells (those containing patient's dna) from the serum - to determine exactly what antigen's a patient has. This is the most sophisticated and accurate method of matching donor/recipient blood. Once a patient's genotype is known, donor blood that contains the same antigens as the patient is safe to use and blood that contains antigens that the patient does not have can be avoided. This way the recipient is not exposed to antigens that he/she does not have - and is less likely to become alloimmunized against it (will not produce allo antibodies against it (allo against foreign blood.) constant exposure to these antigens and formation of allo antibodies can result in auto antibodies.)
Remember the difference between genotype and phenotype. You may have the genotype for green eyes and for brown eyes - but you may have brown eyes. Therefore your genotype is green & brown, but your phenotype is brown. Genotype is all of the genes that you have, whereas Phenotype is what is expressed (what you actually see). For this reason the genotype gives more information then the phenotype. For example, your phenotype for blood may be A + -- however your genotype may be O+ A-, or A+ O- or it can be A+, A+. For more examples see below:
Phenotype Genotype
A AA or A0
B BB or B0
AB AB
0 00
I hope that this makes some sense. I will try to find articles that explain this better than I can. Part of the confusion is probably the fact that I am so wordy - my bad :imsorry
Sharmin
Andy Battaglia:
All I can add is that to put it simply, genotype tells who the real person is, while phenotype tells you who that person and every person who they ever got blood from, is.
Matching the genotype is even more important when the recipient is likely from a different ethnic group than most people in that geographic area. For example, blood donated by Americans of European backgrounds may not be a good match for someone of Asian background, regardless of a phenotype match, so genotyping the blood becomes even more important. It has been recommended that local blood banks make efforts to ensure that they have a range of blood available to match all local ethnic groups for those who will require regular transfusions. It may seem like more trouble but by minimizing or possibly eliminating antibody reactions, the patients ultimately need less blood, so it is worth it to the blood banks to have genotype matching done.
Manal:
Thanks Andy :hugfriend
Thank you so much Sharmin, it is really clear now :hugfriend
But one last question, do blood banks generally do such tests on the blood packs they have or it is just enough for thm to have the blood group and the RH?? I mean if i am the recipent and i have my genotype result, is it a must to have the same test done on the blood packs found in the bank or it is enough to only have mine??
What is the protocol? To m knowlegde, banks screen donors' blood for infectios and diseases and examine the blood type and the RH only
manal
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