Figure 83

In an immunogenetics and transplantation laboratory, three major types of renal pretrans-plantation testing are performed routinely. The human leukocyte antigen (HLA) assignments are assigned by serologic methods (ie, complement-dependent cytotoxicity); however, molecular-based methodologies are becoming widely accepted. Most laboratories now have the capability of reporting at least low-resolution molecular class II types.

The sera of patients awaiting cadaveric donor kidney transplantation are tested for the degree of alloimmunization by determining the percentage of panel reactive antibodies (PRAs). Current federal regulations require that the serum screening test use lymphocytes as targets; however, because these same regulations no longer mandate monthly screening, assays using soluble antigens may be used as adjuncts to the classic lymphocytotoxic assays.

The purpose of cross-match testing is to detect the presence of antibodies in the patients' serum that are directed against the HLA antigens of the potential donor. When present, the antibodies indicate that the immune system of the recipient has been sensitized to the donor antigens. The various test methods differ in sensitivity, including the multiple variations of the lymphocytotoxicity text, flow cytometry, and enzyme-linked immunosorbent assay (ELISA). The degree of acceptable risk is one factor to be considered in selecting a method of appropriate sensitivity. For example, when the only risk considered unacceptable is that of hyperacute rejection, a technique having lower sensitivity is adequate. A second approach may be to consider the degree to which an individual patient or type of patient is at risk for graft rejection. The patient having a repeat graft is at higher risk for graft rejection than is the patient receiving a primary graft. Because patients differ in their degree of risk, it is appropriate to use different techniques to offset that risk.

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