(A) CONSORT diagram of the FIRM trial. (B) After providing written informed consent, 1,997 patients were randomized to receive intravenous (IV) ferumoxytol (n = 997) or ferric carboxymaltose (n = 1,000) on day 0 and 1 week later. Additional study visits occurred at weeks 2 and 5 after enrollment. A subgroup of US-based patients enrolled in the FIRM trial’s nested physiological substudy (ferumoxytol, n = 87; ferric carboxymaltose, n = 98) and underwent more detailed laboratory testing of phosphate homeostasis.