Pre-implantation analysis of kidney biopsies from expanded criteria donors: testing the accuracy of frozen section technique and the adequacy of their assessment by on-call pathologists.

Pre-implantation renal biopsies of expanded criteria donors are one of the criteria used for allocation decisions, but there are concerns about the impact of the interobserver variability and the technique to be used. The aim was (i) to compare the original report performed by on-call pathologists using frozen sections (FS) to a retrospective analysis carried out by a trained pathologist using the same frozen section, and (ii) to compare the same FS to subsequently obtained paraffin sections (PS) by the same pathologist. A total of 92 biopsies, 78 from transplanted and 14 from nontransplanted cases, were analyzed. Agreement between observers using the same FS was weaker than the correlation between FS and PS in all the examined parameters (Kendall's Tau b for the Remuzzi score 0.104 vs. 0.306). According to the Remuzzi score, the revised FS analysis would have resulted in a higher rate of organ discard (n = 19) than PS (n = 14) and the original report (n = 6). However, kidneys that would have been discarded according to the retrospective analysis showed adequate outcomes in terms of graft survival and function. Accordingly, the impact of interobserver and technique-related variability can be minimized by the use of a relatively low threshold (RS ≤ 4) for organ acceptance.