Machine Measured Renal Resistance (MMRR) Is a Surrogate Measure for Renal Allograft Pathology

Abstract

Background: Studies have recognized the relationship among renal allograft resistance, graft function and survival. The relationship of MMRR and chronic allograft pathology remains unstudied. Purpose: To evaluate the relationship among MMRR, renal allograft pathology parameters and renal allograft outcomes. Method: We performed a retrospective analysis of 1181 deceased donor kidneys transplanted in a large donor service area (DSA) from 2007-2009. All kidneys were evaluated using MMRR and Optimized Needle Biopsy Technique protocol. All biopsies were frozen section evaluations performed by a single transplant pathology laboratory for the DSA. The pathology report identified the following renal allograft parameters: 1. Total number of glomeruli/number of obsolete glomeruli (GS); 2. Tubular interstitial scarring (TIS); 3. Intimal fibrous narrowing of arteries (IFN). MMRR was measured after 3 hours of machine perfusion based on previous studies indicating this is the earliest time to predict a difference in graft survival by MMRR cohorts. Based upon MMRR, allografts were separated into three groups: < 0.2, 0.2-0.3, >0.3. Renal function at 1 year was measured using e-GFR (MDRD). ANOVA was used to correlate pre-transplant MMRR with GS, TIS, IFN and 1-year recipient e-GFR. Results: There was no clinical relevance in the difference in GS between the resistance groups. For MMRR < 0.2, 0.2-0.3, and > 0.3, the mean GS% were 4.9271%, 6.1148%, and 5.2624%, respectively. We identified a significant difference in MMRR measured at 3 hours among the TIS groups (Fig 1) (p-value=0.003). For TIS 0-10%, 11-25%, and 26-50%, the mean resistances were 0.2105, 0.2154, and 0.2825, respectively. The difference is significant between the 0-10% and 26-50% groups (p-value =0.0008) and between the 11-25% and 26-50% groups (p-value=0.0024). We have shown previously that there is a significant correlation between MMRR at 3 hours and one year e-GFR (p-value< 0.0001) but not between TIS% and one year eGFR (p-value=0.1772). We found interaction among TIS% and GS% for MMRR groups indicating that GS% directly correlates with TIS % (p-value=0.0018). There is a trend toward significance in the difference between MMRR cohorts for the IFN groups (overall p-value=0.0586). For IFN of 0-10%, 11-25%, >= 26%, the mean resistances were 0.2066, 0.2171, and 0.2254, respectively. There was a trend toward significance in the difference between the 0-10% and 11-25% groups (p-value = 0.0645) and between the 0-10% and >=26% groups (p-value=0.0529).Figure: [MMRR by TIS cohorts at 3 hours]Conclusion: Differences in MMRR measured at 3 hours directly correlate with chronic changes in renal allograft pathology, specifically TIS and to a lesser degree, IFN. MMRR may be a more reliable marker of organ quality and as a means of forecasting one-year renal graft function.