Background Post-transplant polyoma virus nephropathy (PVN) prevalence is 1-10%. Definitive PVN diagnosis requires polyoma virus presence in infected cells, done with immunohistochemical staining for SV40 antigen. The cortical tangential approach (CTA) is a recent technique that has been adopted by many centers. CTA has been reported to increase the yield of cortical tissue for allograft pathologic assessment with fewer complications compared with traditional perpendicular biopsy approach. Its efficacy in the diagnosis of PVN has not been investigated.

Methods 134 renal allograft recipients from 1/2012 to 12/2016 with a total of 195 biopsies via CTA were included in the study. All patients had serum BK DNA PCR and histologic staining for SV40. Biopsies were reviewed for length of cortex, medulla and SV40 positive cells. SV40 density was calculated for each case. Statistics were obtained using chi-square and unpaired t test.

Results All 195 biopsies contained renal cortex (100%) while only 59/195 (30%) contained medullary tissue . The average length of tissue sampled was 16.7mm in the cortex and 6.6 mm in the medulla. The likelihood of a positive SV40 if cortex was sampled was 30% and 51% if medulla was sampled p<0.0001. The SV40 density was much higher in the medulla (19.8 positive cells/mm) compared to the cortex (5.9 positive cells/mm) ( p=0.0003).

Conclusion Renal allograft biopsies using CTA rarely sample medulla. The presence of medullary tissue dramatically increases the likelihood of a positive SV40 stain and PVN diagnosis. Because of the limited medulla sampled, the CTA may decrease the ability to make a pathologic diagnosis of PVN.

CITATION INFORMATION: Abdelwahab D., Khamash H., Kriegshauser S., Heilman R., Smith M. Medullary Tissue Sampling in Renal Allograft Biopsy is More Sensitive for Pathologic Diagnosis of PVN Am J Transplant. 2017;17 (suppl 3).

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