CHAPTER 31: Donor Kidney Scoring Systems

INTRODUCTION

The benefits of renal transplantation for patients with end-stage renal disease on hemodialysis are well established, but currently there is a significant shortage of organs available for transplantation. In an effort to increase the size of the donor pool, donors who may have been excluded from donating previously are currently accepted. However, uses of these marginal kidneys have increased incidence of delayed graft function (DGF) and acute rejection and have resulted in lower graft survival. Several strategies have been proposed to identify the donor risk factors that can affect allograft outcomes. Several donor clinical^1–3 and histopathologic^4,5 scoring systems have been used to predict graft function. This has implications for organ utilization and potential to improve graft survival with proactive modification of immunosuppression.

Biopsy evaluation of donor kidney is particularly important for marginal organs to determine organ suitability. Although significant progress has been made in the field, controversy still remains regarding the value of individual pathologic parameters to predict graft outcome. Currently, donor selection is primarily based on degree of glomerular sclerosis, interstitial fibrosis, and vascular pathology.

MARYLAND AGGREGATE PATHOLOGY INDEX

Maryland aggregate pathology index (MAPI)⁵ is an aggregate pathology score that is based on the evaluation of donor pathologic features that are predominantly related to ischemic and hypertensive injury affecting glomeruli and vessels. The model comprises five pathologic elements and was developed using a large cohort of deceased donor kidneys and validated using a different cohort. The histologic elements that were shown to statistically affect graft outcome included 15% or higher glomerulosclerosis, any degree of arteriolar hyalinosis, arterial sclerosis with a wall-to-lumen ratio in interlobular arteries of more than 0.5 (equivalent to BANFF > cv2 lesion), cortical scar, and presence of periglomerular fibrosis of arterial sclerosis (Figures 31-1A–E). Points were assigned to each of these histopathologic variables based on the hazard ratio for graft loss obtained from Cox proportional hazard univariate analysis (Table 31-1). Interstitial fibrosis was not included in the MAPI score because it did not correlate with graft outcome. Assessment of interstitial fibrosis has poor reproducibility in interobserver and intraobserver variability studies.⁶