*Purpose: Reducing kidney discard is a major priority for the transplant community. While frozen section biopsies are the current standard, they are fraught with technical challenges and unreliable/inconsistent readings. Formalin-fixed samples are more reliable but are not able to be utilized for time-sensitive decisions. When machine perfusion is utilized, kidneys usually are pumped for at least 6 hours. The purpose of our study is to determine if rapid (4-6 hour) formalin-fixed core needle kidney biopsies are feasible and provide reliable data that could assist in the utilization of marginal donors while kidneys remain on the pump, minimizing the effects of the increased cold ischemia time associated with formalin fixation and processing.

*Methods: Donors with a KDPI>85% underwent a wedge kidney biopsy that was then frozen and read by the onsite pathologist at the donor hospital. Decisions regarding use of these kidneys were made at the time of recovery and biopsy. An additional 16-18G core biopsy was performed through the wedge biopsy defect and placed in formalin for subsequent processing. The original frozen section slide and the core biopsy sample were sent to Geisinger where the samples were de-identified. The core biopsy underwent rapid fixation and were then read by a single pathologist. The same pathologist also read the original frozen section slides without knowing the original read, nor the core biopsy result.

*Results: This “proof of concept” study included 23 donors. H&E and trichrome staining required 4 and 6 hours, respectively. 8 of the core samples had >10 glomeruli seen, 5 with > 25 glomeruli. Clinically significant differences were noted between the original and subsequent frozen section readings, as well as the frozen section and core biopsy readings, even in core biopsy samples with <10 glomeruli. Differences in glomerulosclerosis, fibrosis, and vascular disease were enough to potentially influence discard/use of donor kidney grafts (e.g. glomerulosclerosis 18.8% frozen vs 6.7% core, absence of vascular findings on frozen vs severe vascular findings on core, and minimal fibrosis on frozen with moderate-severe on core).

*Conclusions: Rapid formalin-fixed kidney biopsies can be processed within a feasible time frame and provide information that may be considered more reliable than standard frozen section wedge biopsies. Several core samples would be needed to ensure an adequate amount of tissue for assessment. Given the utilization of machine perfusion for marginal kidneys, the additional logistical time (6-8 hrs) required for potentially more reliable biopsies being read by dedicated renal pathologists could reduce the discard of usable kidneys. Additional studies with larger numbers performed in real-time are needed prior to consideration of implementation.

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