The amount of ACE2 present in urine specimens was quantified using a commercial ELISA kit (Cat. No. AG-45A-0022EK-KI01, AdipoGen, Seoul, Korea) according to the protocol provided by the supplier (http://www.adipogen.com/ ag-45a-0022/ace2-human-elisa-kit.html). A standard curve was generated by performing 1:2 serial dilutions of human recombinant ACE2 (50 ng/ml), provided with the kit, with the limit of detection ranging from 0.391 to 25 ng/mL. In preliminary experiments, the average intra-assay coefficient of variation (CV) for the assay was 2.9%, and the average interassay CV value was 8.7% (n = 10). The amount of ACE2 obtained by ELISA was normalized to the subject's urine Cr concentration, and is reported as ng/mg Cr.