In medical terms, PRA stands for Panel Reactive Antibody. It represents the percentage of a panel of different human leukocyte antigen (HLA) types against which a patient's serum contains antibodies. In simpler terms, it measures how reactive a patient's immune system is against potential donor organs or tissues.
Understanding Panel Reactive Antibodies (PRA)
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Purpose: A PRA test is primarily performed to assess the likelihood of a patient rejecting a transplanted organ. It is crucial in determining compatibility between a recipient and a potential donor.
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Mechanism: The test identifies antibodies in the recipient's blood that react against HLA antigens present on cells. HLA antigens are proteins found on the surface of most cells in the body and play a vital role in the immune system's ability to distinguish between "self" and "non-self."
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Test Procedure: The patient's serum is mixed with a panel of cells or purified HLA antigens representing a wide range of HLA types. The percentage of cells or antigens that react with the patient's antibodies is reported as the PRA.
Implications of PRA Levels
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Low PRA: A low PRA (e.g., less than 10%) indicates that the patient has few antibodies against HLA antigens. This suggests a lower risk of rejection and a higher chance of finding a compatible donor.
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High PRA: A high PRA (e.g., greater than 80%) indicates that the patient has a large number of antibodies against HLA antigens. This means a higher risk of rejecting a transplanted organ and makes it more difficult to find a suitable donor. High PRA can result from prior exposure to foreign HLA antigens, such as through previous transplants, blood transfusions, or pregnancies.
Clinical Significance
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Transplant Eligibility: PRA levels are a significant factor in determining a patient's eligibility for transplantation and the type of transplant they can receive.
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Crossmatching: Before transplantation, a crossmatch test is performed to confirm that the recipient does not have antibodies that will react specifically against the donor's HLA antigens. A positive crossmatch indicates an unacceptable incompatibility and contraindicates transplantation.
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Desensitization: In some cases, patients with high PRA may undergo desensitization therapies to reduce their antibody levels and improve their chances of receiving a transplant. These therapies may involve plasmapheresis or intravenous immunoglobulin (IVIg).
Example
Imagine a patient awaiting a kidney transplant. Their PRA test reveals a high percentage (90%). This means they have antibodies against a wide range of HLA types. Finding a kidney that doesn't trigger these antibodies will be difficult, prolonging their wait on the transplant list. The transplant team might consider desensitization protocols to decrease the antibody level and broaden the range of potential donors.
