Research sample collection and analysis
BLOOD
Blood samples were collected either at the time of clinically indicated venipuncture or through existing arterial or central venous line access. If the participant did not have existing lines or planned clinical bloodwork, the study blood sample was not collected. Research blood samples were collected at screening (with additional blood collected at enrollment if the volume from the screening sample was insufficient for all planned analyses), days 1, 2, 3, 7 and hospital discharge for analysis of plasma 25(OH)D and ionized calcium. The research blood samples collected for an ionized calcium concentration were analyzed in real time (unless ionized calcium had been measured through clinical bloodwork in the preceding 24 h). The research blood samples collected to determine plasma 25(OH) concentrations were stored and analyzed in batches by the research laboratory by LC–MS/MS [Urine samples were collected at enrollment, on Day 3, 7, and at hospital discharge and analyzed in in real time for calcium:creatinine ratios.