Table 6.5. Indications for pretransplant native nephrectomy/nephroureterectomy

Large polycystic kidney disease Chronic renal parenchymal infection Chronic infected reflux disease Heavy proteinuria Intractable hypertension Infectious nephrolithiasis with a risk of antibody-mediated hyperacute rejection. There are four components of the immunologic evaluation: ABO blood group antigen determination, HLA typing, serum screening for humoral reactivity to HLA phenotypes, and donor/recipient crossmatching.

a. ABO blood group determination. The ABO blood group antigens are carbohydrate moieties that are expressed on endothelial cells. They are a potential target of recipient circulating preformed cytotoxic anti-ABO antibody. Transplantation across incompatible blood groups may result in humoral mediated hyperacute rejection. Therefore, transplantation is avoided in this circumstance. Several systems of blood group verification are in place at the transplant center and the organ procurement organization to ensure proper ABO matching.

An interesting exceptional circumstance is the possibility of transplanting kidneys from the blood group subtype A2 into type O, B, or AB recipients. It is confirmed that the recipient circulating preformed anti A2 antibody titer is absent. The A2 antigen is weakly immunologic and does not result in induction of antibody. There have also been experimental procedures for ABO incompatible kidney transplants.

b. HLA typing. All transplant recipients are tissue typed to determine the HLA Class I and Class II loci. Multiple alleles exist at each loci, and they are co-domi-nantly expressed by each chromosome. Six HLA antigens are determined. The kidney donors are also HLA typed and the degree of incompatibility between donor and recipient is defined by the number of antigens that are mismatched at each HLA locus. The implications of these results are to determine zero HLA mismatched donor/recipient pairs that allows cadaveric kidneys to be preferentially allocated to those recipients. The degree of mismatching also has implications for the number of points assigned to each transplant recipient on the waiting list for allocation. Finally, HLA matching does influence the outcome of the kidney transplant. For cadaveric kidney transplants the best outcomes are observed in recipients of a zero antigen mismatched kidney. For living related kidney transplantation, the best results are observed in recipients of an HLA- identical kidney allograft. The degree in which HLA mismatching influences outcome varies considerably from center to center, and has changed with the application of the newer immu-nosuppressive agents.

It has been determined that groups of HLA antigens share characteristics in their molecular composition that are related to its antigenicity. These broad specificities have been categorized into cross-reacting groups (CREG). Matching for the CREG groups, rather than the individual HLA antigens, is an alternative method to define the degree of donor/recipient matching. Recipients of CREG matched donor kidneys seldom become sensitized for those specific HLA antigens. There are also advantages to CREG matching in making cadaveric kidney allocation more equitable between races. However, any system of organ allocation using HLA matching as a criterion imposes some degree of racial bias that affects access.

c. Serum screening for antibody to HLA phenotypes. Sensitization to histocompatibility antigens is of great concern in certain populations of transplant candi-

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