Background: BK virus (BKV) infection in renal transplant patients is a constant concern. As BK-induced nephritis may lead to graft failure, detection of the virus is of significant clinical importance. While the diagnosis of BKV infection can be made on H&E stained slides, immunohistochemistry allows for greater detection. The goal of this study was to compare the effectiveness of PCR to conventional (Hematoxylin and Eosin [H&E]) and immunohistochemistry for BKV.  

Design: Sixty-five renal biopsies from renal transplant patients were selected; 26 had definitive histologic and/or immunohistochemistry evidence of BKV and the remaining 39 cases lacked sufficient evidence. DNA extraction was performed and PCR was conducted. In addition, analysis was performed on 49 renal biopsies taken from nontransplanted patients to establish specificity. 

Results: In the 26 cases with BKV infection by H&E/immunohistochemistry, PCR detected BKV in 10 cases (62% sensitivity). In the control group, no evidence of BKV was shown by PCR (100% specificity). Of the 39 cases with suspicion of  BKV but negative H&E/ immunohistochemistry, PCR found 2 cases with BKV. No viral inclusions were seen on H&E, but immunohistochemistry had not been performed. Subsequent immunohistochemistry showed focal BK positivity and   confirmed PCR detection.  

Conclusions: These findings indicate that PCR is a highly specific detection method of BKV, although the sensitivity is low when compared to traditional H&E and 
immunohistochemistry methods. In light of these findings, the use of PCR may be particularly useful in cases with equivocal findings on H&E or immunohistochemistry.