Iron deficiency commonly contributes to the anemia affecting individuals with chronic kidney disease. This review describes diagnostic criteria for iron deficiency in chronic kidney disease, as well as mechanisms of functional and absolute iron deficiency and general treatment principles as delineated in the KDIGO (Kidney Disease: Improving Global Outcomes) guideline. Repletion of absolute iron deficits has progressed over time with the addition of better tolerated, more effective oral agents, including ferric citrate, ferric maltol, and sucrosomial iron. This article examines the structural characteristics and trial data enabling regulatory approval of these novel oral agents. Newer intravenous iron therapies, including ferric carboxymaltose and ferric derisomaltose, allow for fewer infusions and decreased risk of serious hypersensitivity reactions. Concerns about adverse effects such as cardiovascular events and infections are discussed. The potential risk of 6H syndrome (high FGF-23, hypophosphatemia, hyperphosphaturia, hypovitaminosis D, hypocalcemia, and secondary hyperparathyroidism) due to these intravenous agents is emphasized. The proposed pathophysiology of 6H syndrome and hypophosphatemia is described. Ferric pyrophosphate citrate enables administration of iron for repletion through dialysate. Relative merits, costs, and risks of various iron agents such as hypersensitivity and 6H syndrome/hypophosphatemia are summarized.
Keywords: 6H syndrome; Iron; chronic kidney disease (CKD); dialysis; end-stage renal disease (ESRD); ferric carboxymaltose; ferric citrate; ferric derisomaltose; ferric maltol; ferric pyrophosphate citrate; ferritin; ferumoxytol; hemoglobin; iron-deficiency anemia; review; sucrosomial iron; transferrin saturation (TSAT).
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