Endocrine Abstracts

Intravenous iron formulations allow administration of high doses of elemental iron enabling correction of total iron deficit in one or two infusions. An underappreciated complication is hypophosphatemia from increased fibroblast growth factor 23 (FGF-23) secretion. An 85-year-old male presented with a second episode of generalized tonic-clonic seizures. The first episode was a month ago, and serum phosphate was 0.2 mmol/l (0.8-1.4). He was treated with phosphate replacement alone. On this admission serum phosphate was 0.3 mmol/l, adjusted calcium 2.02 mmol/l (2.15-2.6), magnesium 0.86 mmol/l (0.7-1.0), vitamin-D 68 nmol/l and parathyroid hormone (PTH) 85 ng/l (15-65), with an eGFR of 62 ml/min. More than a year ago, he was admitted with melaena and iron deficiency anemia while on dual anti-platelet therapy. CT-Chest-abdomen-pelvis, upper gastrointestinal scopy and capsule endoscopy did not reveal any abnormalities and at that time he received two infusions of Ferric Carboxymaltose (FCM, Ferrinject) to replenish iron stores. He was treated with intravenous phosphate polyfusor and the plan was to use alfacalcidol if the calcium levels fell further, expedite the diagnosis of the cause of gastrointestinal bleeding and to use other intravenous preparations like Ferric Derisomaltose (FDI), that have a lower incidence and severity of hypophosphatemia. To reach the correct diagnosis, clinicians must recognize the typical clinical manifestations of intravenous iron-induced hypophosphatemia and identify a specific pattern of biochemical changes (hyperphosphaturic hypophosphatemia caused by FGF-23, resulting in low 1,25 DHCC, hypocalcemia and secondary hyperparathyroidism). Fractional excretion of phosphate if calculated would be high. Prolonged hypophosphatemia can occur and result in myopathy, osteomalacia and fractures. Physicians should monitor serum phosphate levels in patients receiving repeated doses of specific iron formulations. Identifying people who are at risk, such as those with vitamin D deficiency, might decrease the risk of developing such complications.