Combined detection of urine specific gravity and BK viruria on prediction of BK polyomavirus nephropathy in kidney transplant recipients

Urinary donor-derived cell-free DNA as a non-invasive biomarker for BK polyomavirus-associated nephropathy

BK polyomavirus-associated nephropathy (BKPyVAN) is a common cause of allograft failure. However, differentiation between BKPyVAN and type I T cell-mediated rejection (TCMR) is challenging when simian virus 40 (SV40) staining is negative, because of the similarities in histopathology. This study investigated whether donor-derived cell-free DNA (ddcfDNA) can be used to differentiate BKPyVAN. Target region capture sequencing was applied to detect the ddcfDNAs of 12 recipients with stable graft function, 22 with type I TCMR, 21 with proven BKPyVAN, and 5 with possible PyVAN. We found that urinary ddcfDNA levels were upregulated in recipients with graft injury, whereas plasma ddcfDNA levels were comparable for all groups. The median urinary concentrations and fractions of ddcfDNA in proven BKPyVAN recipients were significantly higher than those in type I TCMR recipients (10.4 vs. 6.1 ng/mL, P<0.001 and 68.4% vs. 55.3%, P=0.013, respectively). Urinary ddcfDNA fractions (not concentrations) were higher in the BKPyVAN-pure subgroup than in the BKPyVAN-rejection-like subgroup (81.30% vs. 56.64%, P=0.025). With a cut-off value of 7.81 ng/mL, urinary ddcfDNA concentrations distinguished proven BKPyVAN from type I TCMR (area under the curve (AUC)=0.848, 95% confidence interval (95% CI): 0.734 to 0.963). These findings suggest that urinary ddcfDNA is a non-invasive biomarker which can reliably differentiate BKPyVAN from type I TCMR.

Relationship between urine specific gravity and the prevalence rate of kidney stone

Background

The purpose of this study was to evaluate the relationship between urine specific gravity (USG) and the prevalence rate of kidney stone.

Methods

We conducted a cross-sectional study of adult participants (≥20 years) of the National Health and Nutrition Examination Survey (NHANES) from 2007 to 2008. The USG was divided into three groups: <1.008, 1.008-1.020 and >1.020. Univariate and multivariate logistic regression analysis was used to determine the effect of USG on the prevalence rate of kidney stone.

Results

A total of 4,791 patients were included in this study, of which 464 (9.7%) reported a history of kidney stone. Univariate logistic regression analysis showed that age, gender, race, hypertension, diabetes, body mass index (BMI), estimated glomerular filtration rate (eGFR), USG and urine creatinine were closely related to the prevalence of kidney stones. After adjusting for known confounding factors, multivariate logistic regression showed that the prevalence rate of kidney stone increased with the increase of USG (1.008-1.020 vs. <1.008, OR =1.31, 95% CI, 0.09-1.91, P=0.155; >1.020 vs. <1.008, OR =1.71, 95% CI, 1.16-2.54, P=0.007).

Conclusions

The increase of USG was significantly correlated with self-reported kidney stone. This finding helps to identify risk factors for kidney stones as early as possible in the United States.