The main objectives of this study were (i) to undertake serial measurements of 25(OH)D and 1,25(OH)2D concentrations in critically ill patients with and without moderate to severe AKI; (ii) to investigate whether there are differences in vitamin D metabolite concentrations between AKI patients who recover renal function and those without recovery; and (iii) to investigate the role of factors that usually impact vitamin D regulation, including gender, annual season, ionized calcium (iCa), Magnesium (Mg) and PTH [12]. Here, PTH is linked to acute kidney injury.