目的  探讨影响BK病毒（BKV）相关性肾病（BKVAN）的肾移植受者病毒清除的因素，分析病毒清除过程对移植肾功能及长期预后的影响。方法  入选通过移植肾穿刺活检并结合尿沉渣Decoy细胞计数，尿、血标本中BK病毒DNA含量的测定，确诊的BKVAN 49例，进行减少免疫抑制剂强度的治疗，并定期监测BKV的活动及移植肾功能。根据BKV（包括Decoy细胞、BKV尿症和BKV血症）有无清除，将BKVAN受者分成清除组与未清除组，比较两组间和组内确诊时、调药后6和12个月血清肌酐的差异及两组间各项临床指标的差异。应用Kaplan-Meier方法计算BKV清除所需时间及移植肾1、3、5年存活率，应用Log-Rank检验比较BKV清除组与未清除组移植肾存活率的差异。结果  BKVAN受者在降低免疫抑制强度后Decoy细胞、BKV尿症、BKV血症清除率为63.8%、27.7%和80.5%。Kaplan-Meier方法计算Decoy细胞、BKV尿症和BKV血症清除所需中位时间分别为11、41和5个月。是否术后规律监测BKV影响病毒的清除(P<0.05)。BKV清除组调药后6和12个月的血清肌酐较确诊时有所下降或无明显差异，而未清除组相应的肌酐水平有所上升。两组间比较6和12个月与确诊时血清肌酐差值，BKV清除组低于未清除组(P<0.05)。调药后所有BKVAN受者均无急性排斥反应的发生。BKVAN受者移植肾1、3和5年存活率分别100%、83.4%和66.4%。 BKV清除组的移植肾1、3和5年存活率明显高于相应的未清除组（P<0.05）。结论  术后规律监测BKV、早期移植肾活检发现BKVAN有利于BKV的清除，而病毒能否被清除影响移植肾功能及长期存活率。

Objective  To investigate the factors affecting BK virus (BKV) clearance and analyze the effect of the course of viral clearance on graft function and long-term prognosis of renal transplant recipients with BK virus associated nephropathy (BKVAN). Methods  Forty-nine cases of BKVAN confirmed by renal transplant biopsy, quantitative assay of urine cytology, and detection of DNA levels of BKV in urine and blood were selected. Patients underwent reduction of maintenance immunosuppression and the activity of BKV and renal function were monitored regularly. According to the clearance of BKV (including Decoy cell, viruria, and viremia), patients were divided into the clearance group and non-clearance group. Differences of serum creatinine between two groups and within group at diagnosis and 6 and 12 months after reduction of immunosuppression were compared. Differences of clinical indexes between two groups were also compared. The viral clearance time and 1-, 3-, and 5-year graft survival rates were calculated by Kaplan-Meier curves and the difference of graft survival rates between two groups were compared by Log-rank test. Results  The clearance rates of Decoy cell, viruria, and viremia of recipients with BKVAN after reduction of maintenance immunosuppression were 63.8%, 27.7%, and 80.5%, respectively. The median clearance time of Decoy cell, viruria, and viremia calculated by Kaplan-Meier curves was 11, 41, and 5 months, respectively. Regular monitoring of BKV after surgery affected the viral clearance (P<0.05). The serum creatinine levels of the clearance group 6 and 12 months after reduction of immunosuppression were lower than or almost the same as those at diagnosis, while the serum creatinine levels of the non-clearance group 6 and 12 months after reduction of immunosuppression were higher than those at diagnosis. The difference of serum creatinine levels of the clearance group between 6 and 12 months after reduction of immunosuppression and at diagnosis were smaller than those of the non-clearance group (P<0.05). No acute rejection was observed after reduction of immunosuppression. The 1-, 3-, and 5-year graft survival rates of patients with BKVAN were 100%, 83.4%, and 66.4%. The 1-, 3-, and 5-year graft survival rates of the clearance group were significantly higher than those of the non-clearance group (P<0.05). Conclusion  Regular monitoring of BKV after surgery and detection of BKVAN by early renal transplant biopsy is helpful for the clearance of BKV, which can affect the function and long-term survival rate of grafts.