简介：AbstractBackground:BK polyomavirus (BKPyV)-associated nephropathy (BKPyVAN) is an important cause of dysfunction and failure of renal transplants. This study aimed to assess the diagnostic performance of morning urine specific gravity (MUSG) in diagnosing BKPyVAN in kidney transplant recipients.Methods:A total of 87 patients, including 27 with BKPyVAN, 22 with isolated BKPyV viruria, 18 with T cell-mediated rejection(TCMR), and 20 with stable graft function, were enrolled in the First Affiliated Hospital of Sun Yat-Sen University from March 2015 to February 2017. MUSG at biopsy and during a follow-up period of 24 months after biopsy was collected and analyzed. Receiver operating characteristic (ROC) curve analysis was used to determine the ability of MUSG to discriminate BKPyVAN.Results:At biopsy, the MUSG of BKPyVAN group (1.008 ± 0.003) was significantly lower than that of isolated BK viruria group(1.013 ± 0.004, P < 0.001), TCMR group (1.011 ± 0.003, P = 0.027), and control group (1.014 ± 0.006, P < 0.001). There was no significant difference in MUSG among the isolated BK viruria group, TCMR group, and control group (P = 0.253). In BKPyVAN group, the timing and trend of MUSG elevate were consistent with the timing and trend of the decline of viral load in urine and plasma, reaching a statistical difference at 3 months after treatment (1.012 ± 0.003, P < 0.001) compared with values at diagnosis. ROC analysis indicated that the optimal cut-off value of MUSG for diagnosis of BKPyVAN was 1.009, with an area under the ROC curve (AUC) of 0.803 (95% confidence interval [CI]: 0.721–0.937). For differentiating BKPyVAN and TCMR, the optimal MUSG cut-off value was 1.010, with an AUC of 0.811 (95% CI: 0.687–0.934).Conclusion:Combined detection of MUSG and BKPyV viruria is valuable for predicting BKPyVAN and distinguishing BKPyVAN from TCMR in renal transplant recipients.