Blood tests give kidney matches the best chance of success
When singer Selena Gomez posted pictures of herself on social media post-kidney transplant, systemic lupus erythematosus (SLE) and kidney transplants started trending. Gomez has been open about her diagnosis of SLE and her struggle with this autoimmune disease. When it affects the kidneys it’s known as lupus nephritis and sometimes leads to a kidney transplant.
Regardless of the reason why a kidney transplant is needed, Dr Heather Dunckley, Clinical Scientist and ASHI Director, Tissue Typing, at the New Zealand Blood Service, said pathology tests to find the best donor kidney match are the same for everyone. These include four key blood tests that determine if the kidney recipient and donor are a suitable match before the transplant.
ABO blood grouping is carried out and donor-recipient compatibility is assessed following the same rules as for blood transfusion. For example, if the recipient’s blood type is A, they can receive a kidney from donors with the blood types A and O. If the donor’s and recipient’s blood types are compatible then three more blood tests follow - tissue typing, antibody screening and cross matching.
Despite the name, tissue typing is a blood test for human leukocyte antigens (HLA). “We extract the DNA from the recipient’s and donor’s blood sample to identify the major HLA genes and the corresponding proteins (antigens) that are found on most cells in the body,” explained Dr Dunckley.
These proteins, or markers, are inherited from our parents and are a unique signature. They help the body’s immune system discriminate between a person’s own cells (‘self’) and those that are foreign or ‘non-self’. The cells recognised as ‘non-self’ can trigger an immune response, and this is why it’s important to match these HLA proteins as closely as possible between the donor and transplant recipient.
“If the donor and recipient have the same HLA types then the immune system of the recipient is less likely to initiate an immune response against the transplanted kidney. We also perform an antibody screen on the recipient to check they have no anti-HLA antibodies against the donor,” said Dr Dunckley.
The fourth test is a crossmatch.
“This is where we isolate the lymphocytes from the donor’s blood and incubate them with the recipient’s serum (a component of blood) and look for a reaction. If there is a positive reaction then it can stop the transplant from taking place. This is because there is a factor in the recipient’s serum that can react against the donor kidney cells as the blood goes through the kidney, potentially causing rejection. We won’t always know why the crossmatch test is positive, only that there is a reaction that could cause a problem,” she explained.
Dr Dunckley said blood tests to monitor for anti-HLA antibodies after the kidney transplant are performed at scheduled intervals.
“An HLA antibody test will usually be immediately requested if there are any signs of the transplanted kidney being rejected. The patient’s clinician may also request additional tests including a kidney biopsy to assess the condition of the kidney’s cells.”
Kidney donors can be deceased or living donors related or unrelated to the recipient.
“In the case of an unrelated living donor, they may be a friend or they may be an anonymous altruistic donor unknown to the patient who has decided they would like to donate a kidney to a patient in need. The tissue typing and matching process is the same whether the donor is deceased, related or unrelated. In the case of an altruistic donor, they will donate to the best-matched patient on the kidney waiting list,” said Dr Dunckley.
Despite all human kidneys being anatomically similar, they can’t be successfully transplanted into other people without the information collected from these key blood tests. While not every recipient receives a perfect kidney match, the blood test’s information provides the vital road map for the greatest transplant success.
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This article appeared in the October 2017 Edition of ePathWay which is an online magazine produced by the Royal College of Pathologists of Australasia (http://www.rcpa.edu.au/Library/Publications/ePathway).
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