Urine cfDNA Extraction and Purification

Urine cfDNA was prepared from 22 to 90 mL of urine with Q-sepharose resin slurry (GE Healthcare, Chicago, Illinois, USA) at a ratio of 10 μL slurry per mL of urine and mixed as previously described [28 (link),35 (link)]. After 30 minutes, the urine/resin mixture was centrifuged for 10 minutes at 1,800 g. The supernatant was discarded, and resin was washed twice with 0.3 M LiCl/10 mM sodium acetate (pH 5.5), applying 2 mL per 100-μL resin. The resin was then transferred to a Micro Bio-Spin column (Bio-Rad, Hercules, California, USA), and the bound material was eluted by adding 3 separate 670-μL aliquots of 2 M LiCl/10 mM sodium acetate (pH 5.5). Next, the eluates were combined in 70% ethanol and passed over a QIAquick column (Qiagen, Hilden, Germany). The column was washed with 5 mL of 2 M LiCl in 70% ethanol, followed by 5 mL of 75 mM potassium acetate (pH 5.5) in 80% ethanol. We removed residual liquid by centrifuging the columns at 20,000 g for 3 minutes. Finally, bound DNA was eluted into 50 μL of nuclease-free water or 10 mM Tris-Cl (pH 8.5). DNA concentrations were measured using a Qubit dsDNA HS Assay Kit and Qubit 4.0 Fluorometer (Thermo Fisher Scientific, Waltham, Massachusetts, USA).