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To analyze the risk factors affecting BK virus associated nephropathy (BKVAN) after kidney transplantation.Three screening methods for BKVAN including quantitative PCR assay for BK virus (BKV) DNA load in urine and plasma and quantitative assay of urine cytology concurrently with renal transplant biopsies for the evaluation of 615 patients from January 2006 to December 2014 were used. The renal allograft biopsy specimens were analyzed by routine histologic examination, immunohistochemistry and classified into three categories of BKVAN. Potential variables were analyzed by Logistic regression model multivariate analysis to assess and rank BKVAN related risk factors.The positive rate of urine decoy cell , BKV viruria and viremia in 615 renal recipients were 13.7% (84/615), 29.3% (180/615), and 8.8% (54/615), respectively. BKVAN were diagnosed in 49 recipients. The incidence and the median level of the number of the decoy cell, BK viral load in urine and plasma were higher in the BKVAN group than those in non-BKVAN group (all P0.05). Tacrolimus (Tac) combined with mycophenolic acid (MPA) protocol (OR=12.4, P=0.001) and severe pneumonia post-transplant (OR=3.7, P=0.001) were the independent risk factors impacting on BKVAN in renal recipients.The renal recipients with high level of BKV replication, whose immunosuppressant protocol include Tac and MPA, should be suspected the diagnosis of BKVAN.

To observe the clearance of BK viruria and long-term graft survival in renal transplant recipients with BK virus (BKV) infection under the protocol of our center.Urine was taken from 229 renal transplant recipients,who were transplanted between March 2006 to October 2008, for BKV cytological testing and real-time PCR for BKV DNA at 1, 3, 6, 9, and 12 months after transplantation. Graft biopsies were analyzed for SV40-T by immunohistochemical method. Recipients were treated according to the BKV infection protocol of our center and were monitored for BKV and graft function. All the patients were followed for at least 5 years.By 1 year post-transplant, urinary decoy cells, BK viruria, and BKV associated nephropathy (BKVAN) occurred in 78, 99, and 7 patients, respectively. The median followed-up time was 63.6 (3.0-88.0) months. After reduction of immunosuppression, 81 (81.8%) patients cleared BK viruria with a mean time of (12.1 ± 1.9) months. When compared with non-BKVAN patients, BKVAN patients had a higher median peak level of BK viruria (2.07 × 10⁹ vs 9.28 × 10⁵ copies/ml, P=0.002), lower frequency of clearance (3/7 vs 78/92, P=0.006), longer BK viruria clearance time ((45.4 ± 6.4) vs (8.7 ± 1.5) months, P=0.001). The 1, 3, 5-year graft survival in BK viruria patients were 99.0%, 95.9% and 89.6% respectively, which were not significantly different from those in non-BK viruria patients (97.7%, 95.5% and 93.7%, P=0.289). Graft function of BK viruria patients were not statistical significance compared with non-BK viruria patients (serum creatinine level 5 years post-transplant: (105.7 ± 30.9) vs (111.3 ± 4.6) µmol/L, P=0.322). Graft function of BKVAN patients at 5 years post-transplant was stable without significantly difference from non-BKVAN patients (serum creatinine level: (127.6 ± 41.0) vs (108.3 ± 39.3) µmol/L, P=0.204).On the premise of intensively and regularly BKV monitoring and preemptive reduction of immunosuppression, BK viruria and BKVAN can not impact on the long-term graft survival in renal transplant recipients.