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Abstract: FR-PO579

Symptomatic Hypophosphatemia from Parenteral Iron Administration

Session Information

  • Trainee Case Reports - III
    October 26, 2018 | Location: Exhibit Hall, San Diego Convention Center
    Abstract Time: 10:00 AM - 12:00 PM

Category: Trainee Case Reports

  • 902 Fluid and Electrolytes: Clinical


  • Zahid, Sohaib, Allegheny Health Network, Pittsburgh, Pennsylvania, United States
  • Lavudi, Swathi, Allegheny Health Network, Pittsburgh, Pennsylvania, United States
  • Sureshkumar, Kalathil K., Allegheny Health Network, Pittsburgh, Pennsylvania, United States
  • Ko, Tina Y., Allegheny Health Network, Pittsburgh, Pennsylvania, United States

Group or Team Name

  • AGH Nephrology

Fibroblast growth factor 23 (FGF23) plays a crucial role in phosphate and vitamin D homeostasis. Herein we present a case of severe symptomatic hypophosphatemia following the administration of intravenous (IV) ferric carboxymaltose likely triggerred by inappropriate FGF23 activity.

Case Description

A 31 year old female received two doses of IV ferric carboxymaltose for iron deficiency anemia. Four days later, she presented with numbness, tingling and muscle cramps. Evaluation revealed severe hypophosphatemia with serum phosphorus level of 1.0 mg/dl. Serum potassium, calcium, iPTH, 25 hyrdoxy, and 1,25 dihydroxyvitamin D levels were normal. A 24 hour urine collection revealed calcium of 27 mg (100 -250mg) and phosphorus of 1.8 g (0.4- 1.3 g) with a high fractional excretion of phosphorus >5%. Serum FGF23 level was inappropriately elevated at 97 RU/ml (44-215) for the degree of hypophosphatemia. Patient was given IV and oral phosphorus supplementation repeatedly without clinically significant improvement. Serum phosphorus levels were normalized with resolution of symptoms three weeks later.


FGF23 is secreted primarily by bone, thymus, heart, brain and, in low levels, by several other tissues. It reduces serum phosphorus levels by decreasing expression of type IIa sodium/phosphate cotransporters, resulting in decreased renal phosphate reabsorption. It also down regulates the gene transcription of 1α-hydroxylase thereby reducing the bioactive 1,25-dihydroxy vitamin D (1,25-2OH-VitD) further decreasing the phosphate reabsorption in the gut.
Ferric carboxymaltose is a newer iron formulation increasingly prescribed due to its effectiveness and shorter infusion time. There have been reports of hypophosphatemia associated with use of IV iron preparations including saccharated ferric oxide and ferric citrate hydrate. Studies have shown that IV iron may reduce peripheral degradation, secretion, and clearance of FGF23 resulting in inappropriately elevated FGF23 levels. Data is scarce with use of IV ferric carboxymaltose and hypophosphatemia.
Our case highlights the importance of understanding the side effect profile of commonly administered medications and formulations so that an early diagnosis could be established.