This is a sensitive, high-throughput immunoassay that uses Luminex technology to detect and characterize the pattern and level of antibodies directed against human leukocyte antigens (HLA) in a patient's blood. It measures the negative immunocompatibility ratio (PRA) by exposing the patient's serum to a panel of granules coated with different HLA antigens, thus providing an accurate estimate of the risk of graft rejection.