Quantitative detection of BK virus in kidney transplant recipients: a prospective validation study

Abstract Introduction: BK virus (BKV) infection in renal transplant patients may cause kidney allograft dysfunction and graft loss. Accurate determination of BKV viral load is critical to prevent BKV-associated nephropathy (BKVAN) but the cut-off that best predicts BKVAN remains controversial. Objective: To evaluate the performance of a commercial and an in-house qPCR test for quantitative detection of BK virus in kidney transplant recipients. Methods: This was a prospective study with kidney transplant recipients from two large university hospitals in Brazil. Patients were screened for BKV infection every 3 months in the first year post-transplant with a commercial and an in-house real time polymerase chain reaction (qPCR) test. BKVAN was confirmed based on histopathology. The area under the curve for plasma qPCR was determined from receiver operating characteristic analysis. Results: A total of 200 patients were enrolled. Fifty-eight percent were male, 19.5% had diabetes mellitus, and 82% had the kidney transplanted from a deceased donor. BKV viremia was detected in 32.5% and BKVAN was diagnosed in 8 patients (4%). BKVAN was associated with viremia of 4.1 log copies/mL, using a commercial kit. The cut-off for the in-house assay was 6.1 log copies/mL. The linearity between the commercial kit and the in-house assay was R2=0.83. Conclusion: Our study shows that marked variability occurs in BKV viral load when different qPCR methodologies are used. The in-house qPCR assay proved clinically useful, a cheaper option in comparison to commercial qPCR kits. There is an urgent need to make BKV standards available to the international community.

摘要 研究背景：BK病毒（BK virus，BKV）感染可导致肾移植患者出现移植肾功能不全乃至移植物失功。精准检测BKV病毒载量对于预防BK病毒相关性肾病（BKV-associated nephropathy，BKVAN）具有关键意义，但目前预测BKVAN的最佳临界值仍存在争议。

目的：评估商用及自研实时荧光定量聚合酶链反应（real time polymerase chain reaction，qPCR）检测方法在肾移植受者BK病毒定量检测中的性能表现。

方法：本研究为一项前瞻性研究，纳入来自巴西两所大型高校附属医院的肾移植受者。移植后第一年每3个月采用商用及自研实时荧光定量聚合酶链反应（qPCR）对患者进行BKV感染筛查。BKVAN的确诊依据组织病理学检查结果。通过受试者工作特征曲线（receiver operating characteristic，ROC）分析确定血浆qPCR检测的曲线下面积。

结果：本研究共纳入200例患者。其中58%为男性，19.5%合并糖尿病，82%的移植肾脏来自已故供体。32.5%的患者检测到BKV病毒血症，8例患者（占比4%）确诊为BKVAN。采用商用试剂盒检测时，BKVAN与4.1 log拷贝/毫升的病毒血症水平相关；自研检测方法的临界值为6.1 log拷贝/毫升。商用试剂盒与自研检测方法的线性相关系数R²=0.83。

结论：本研究结果显示，采用不同的qPCR检测方法时，BKV病毒载量存在显著差异。自研qPCR检测方法具有临床应用价值，且相较于商用qPCR试剂盒成本更低。国际社会亟需统一BKV检测的标准物质。