Donor Kidney Assessment-Functional Metrics and Biomarkers During Ex Situ Machine Perfusion

The shortage of suitable donor kidneys remains a major challenge in transplantation. To address this shortage, kidneys from circulatory death donors and donors who do not meet the standard criteria are increasingly used. However, such kidneys are associated with poorer posttransplant outcomes and would therefore benefit from robust pretransplant evaluation. Machine perfusion technology enables noninvasive, real-time evaluation of kidney grafts through functional measurements and biomarker analysis in the circulating perfusate and urine. These measurements have the potential to determine kidney graft quality before transplantation and potentially predict posttransplant outcomes. However, reliable evaluation tools are not yet well-established and approximately 18% of donor kidneys are still ultimately discarded based on subjective assessments. Evidence indicates that physiological and biochemical parameters, such as renal blood flow and endocrine function, can be used to assess graft quality objectively. Additional perfusate biomarkers identified include immune mediators, markers of cellular stress, injury and death, metabolic biomarkers, and imaging-based assessments. This review highlights a diverse range of perfusion parameters, as well as urinary and perfusate biomarkers that may give valuable information about donor kidney quality and possibly associate with posttransplant outcomes. Nonetheless, most markers have not yet been clinically validated, and their predictive value for posttransplant outcomes remains uncertain. Standardized study designs and integration of multiple quality assessment parameters are essential to advance donor kidney assessment.