Background: Banff 2013 criteria recommends performing ultra-structural studies with electron microscopy (EM) in most kidney transplant (KT) biopsies if the technology is available. We aimed to determine the impact of EM results on enhancing diagnostic findings in pediatric KT biopsies performed at our center.

Methods: All KT biopsy reports since routine EM use started on 1 June 2014, until 31 October 2016 were reviewed. We evaluated the number of biopsy cores, transplant complications, light microscopy (LM) and EM findings in each case. Our primary end point was the positive yield rate of EM use defined as an upgraded diagnosis based on EM findings relative to LM.

Results: 80 unique KT biopsy reports were reviewed. There were 4 protocol biopsies and 76 for cause (90% had elevated creatinine, 50% had a positive DSA, 5% had suspected FSGS recurrence). Biopsies were obtained at a median of 144 weeks post transplant (range 1-921). A median of 2 cores were obtained per biopsy (range 2-5). EM studies were completed for 61 biopsies (76%). Reasons for not completing EM included no glomeruli on EM core (5 cases), or no core submitted for EM per MD discretion (14 cases). Biopsies where EM was not performed did not significantly differ from those were EM was completed in terms of total cores obtained or number of glomeruli on LM. Complication rate was low (3.7%) with 2 counts of gross hematuria and 1 perinephric hematoma.

In 61 biopsies where EM was completed, EM findings included foot process fusion (62%), endothelial cell swelling (38%), subendothelial lucencies (31%), and glomerular basement membrane duplication/ transplant glomerulopathy (TG) (41%). EM findings were critical to immediate management in 3 cases (due to FSGS recurrence). In the remaining 58 cases, there was a positive yield of 31% where 18 biopsies were upgraded to a worse category after identification of TG on EM. An upgraded diagnosis of TG was not associated with DSA or elevated creatinine preceding biopsy, however, biopsies with TG on EM tended to be performed further out from transplant relative to those without TG (median 206 vs 130 wks, p value 0.07).

Conclusion: Routine EM use in analyzing pediatric KT biopsies at our institution proved safe and provided valuable additional diagnostic information in almost one third of cases that otherwise would not be predicted based on clinical variables (DSA, creatinine and time since transplant). Further follow-up to determine if early EM TG identification affects long-term outcomes is needed.

CITATION INFORMATION: Grodsky J, Craver R, Ashoor I. Utility of Electron Microscopy in Kidney Transplant Biopsies. Am J Transplant. 2017;17 (suppl 3).

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