This study will incorporate data from subjects' first ever peritoneal equilibrium test (PET), changes in the transfer of water across the peritoneal membrane over time, demographic information, and results from laboratory analysis of DNA, blood, and dialysate. The investigators hope that this study will provide information on the biological pathways that account for variability in the peritoneal membrane. This could ultimately lead to the development of biomarkers to identifying individuals at risk for decline in peritoneal membrane function over time and/or be used to identify novel therapeutic targets to preserve or enhance membrane function. Identifying the biological pathways will also increase the understanding of vascular biology, angiogenesis, and fibrosis that could be applied to other tissues and other diseases.