Panel Reactive Antibodies (PRA) is a laboratory test used to detect the presence of antibodies in a patient's blood against specific antigens. This test is particularly important before organ transplantation, as it helps assess the degree of tissue compatibility between the donor and recipient. The higher the level of antibodies, the greater the likelihood of an immune reaction against the transplanted organ, which could lead to rejection. The test is also used in certain cases to evaluate some autoimmune diseases. It helps doctors make informed decisions about transplantation and ensure the best possible outcomes for patients.