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The expanded criteria donor is any donor over the age of 60 years or a donor over the age of 50 years with 2 of the following 3 items: (1) history of high blood pressure, (2) serum creatinine ≥1.5 mg/dL, and (3) death due to stroke. To accept an expanded criteria donor kidney may significantly decrease the amount of time a person waits for transplant but requires written informed consent from the recipient. Although expanded criteria donor kidneys have predictably shorter outcomes than standard criteria donors, the exact risk is unknown. At 5 years follow-up, 50% of expanded criteria donor kidneys are still working. Regardless of donor status of these kidneys as expanded criteria or standard criteria, the transplant recipients have higher survival rates compared with candidates who remain on the wait list. The success rate may be increased when a perfusion pump is used to preserve the kidneys. Sometimes the function of a single kidney from an expanded criteria donor is deemed insufficient. In this situation, a pair of marginally functioning kidneys may be transplanted as a dual-kidney transplant. This dual transplant option offers acceptable outcomes as good as a single-kidney transplant with normal function and can effectively address the shortage of donor organs. The use of a perfusion pump allows the clinician to decide whether or not to use a particular expanded criteria donor kidney. Expanded criteria donors may be justified by meticulous selection of each donor for recipients, along with more sophisticated surgical techniques to maximize the kidney donor pool.

Monitoring allograft function after kidney transplant has routinely relied on the use of nonspecific markers, such as serum creatinine, glomerular filtration rate, proteinuria, and donor-specific antibodies. These traditional markers have low sensitivity and fail to detect subclinical changes. Diagnosis of renal allograft dysfunction still requires an allograft biopsy, as it remains the criterion standard for assessment of graft status. However, renal biopsy is an invasive procedure, and sampling errors may result in misdiagnosis, perhaps causing graft failure. New biomarkers have been developed to monitor allograft function, although many are not yet routinely used. Other shortcomings, such as lack of standardization and high cost, should be solved before their widespread application in the clinic. A recipient's immune status could be monitored by use of urine or blood samples. These include functional cell-based assays and the evaluation of molecular expression at the messenger RNA or protein levels. Molecular technologies, including molecular microscope diagnostic systems, have been recently developed to improve the yield of histologic evaluation of the allograft biopsy. Prospective, interventional trials are required to demonstrate whether these new biomarkers improve patient or transplant outcomes. Implementation of these technologies into standard clinical practice remains challenging until their generalizability, cost, ease of interpretation, and the identification of patients who may benefit from more than standard-of-care surveillance can be determined. These biomarkers could allow immunosuppressive therapy to be individualized for patients.

Recent developments have been achieved for better matching in solid-organ transplantation by epitope matching. HLA matching remains a standard immunologic strategy to determine organ compatibility for recipients. Advancements in tissue typing have introduced HLA matching at the epitope level. For this, B cells are able to recognize polymorphic amino acid configurations, which are named epitopes. However, antibody production against these epitopes may be a leading cause of rejection. Although data to support the added clinical benefit of epitope matching over traditional antigen matching are still lacking, there are at least 2 theoretical reasons for epitope matching: (1) to avoid future allosensitization with the development of anti-HLA antibodies and (2) to allow selection of a suitable allograft for highly sensitized patients through virtual crossmatch. Sensitive antibody tests with a comprehensive panel of single alleles have yielded informative, donor-specific antibody reactivity patterns that can be analyzed with a computer algorithm. This program (HLAMatchmaker) uses structurally defined eplets to describe epitopes that can react with specific antibodies. Although low mean fluorescence intensity levels by Luminex (Austin, TX, USA) assay are usually considered low risk for solid organ transplant, it could be important in posttransplant humoral rejection. Thus, specific shared eplets should always be investigated with respect to previous transplant mismatches. Epitopes are present on a single HLA (private epitope) or shared by multiple antigens (public epitope). The phenomenon of crossreactivity in HLA testing, often explained as crossreactive groups of antigens with antibody, can be clearly explained now by public epitopes, an antibody targeting an epitope that shows positive reaction with all antigens sharing the epitope. A better understanding of the immunogenicity and structural characteristics of HLA epitopes will guide us to consider epitope matching as an important parameter for donor selection in kidney transplant in the near future.