Category: Calcium/Bone Disorders

Monitor: 31


Friday, Apr 26
12:00 PM – 12:30 PM

Objective : Intravenous (IV) iron therapy for iron deficiency anemia (IDA) is becoming more popular among patient and providers due to its low side-effect and toxicity profiles. Some IV iron preparations have been recognized to cause hypophosphatemia in case reports; therefore, it is always key to gather an accurate medication history in patients presenting with this problem.

Methods : N/A

Results : N/A

Discussion :

51-year-old African-American female with past medical history of myasthenia gravis status-post thymectomy in whom Endocrinology was consulted for recurrent episodes of hypophosphatemia. One year ago, she presented to the hospital with generalized weakness, muscle spasms and dyspnea with laboratory evidence of  severe hypophosphatemia (0.8 mg/dL), vitamin D deficiency (6 ng/mL) and elevated PTH (114 pg/mL); she was started on appropriate supplementation. Nonetheless, she presented 3 weeks later with persistent symptoms. Workup this time showed phosphorus (P) 1.4 mg/dL, improved 25-OH vitamin D at 34.9 ng/mL, and PTH 103 pg/mL. Fractional excretion of phosphate was elevated (84.5%), while tubular reabsorption of phosphorus (TRP) and maximal tubular reabsorption of phosphorus per glomerular filtration rate (TmP/GFR) were significantly decreased (16% and 0.22 mmol/L, respectively). Patient was discharged on higher doses of oral phosphorus and was lost to follow-up. Nine months later, she returned to clinic with recurrent symptoms and a P of 1.2 mg/dL. Only new history obtained was a recent transfusion of ferric carboxymaltose (FCM); on further questioning, she recalled receiving this medication prior to her first occurrence. TmP/GFR was again low at 0.4 mmol/L and FGF23 was elevated (184 RU/mL). Replacement therapy was started and patient was instructed to avoid FCM in the future.

Increasing evidence shows that both IDA and its treatment with certain IV iron preparations can cause hypophosphatemia with long-term complications such as osteomalacia or fractures with repeated administration. IDA is associated with elevated FGF23 levels; however, this is well regulated via FGF23 cleavage by osteocytes. On the other hand, some IV iron formulations like FCM inhibit cleavage of the active hormone intact FGF23 (iFGF23), leading to increased concentrations with concurrent hypophosphatemia.

Conclusion :

Severe hypophosphatemia can occur after administration of FCM, especially in patients with normal renal function. Providers should always be aware of this important side effect and always screen for recent administration in any patient with hypophosphatemia, as avoidance of the implicated agent can prevent future complications.


Ashkan M. Zand

Endocrinology Fellow
Houston Methodist Hospital
La Porte, Texas

Ashkan Michael Zand is currently the chief fellow at the Houston Methodist Endocrinology Fellowship program. As a native Texan, Dr. Zand attended the University of Houston in which he acquired a B.A in Chemistry and B.S. in Biology. Afterwards, Dr. Zand underwent his medical education at the University of Texas Medical Branch at Galveston where he completed his medical degree and Internal Medicine residency.

Gonzalo J. Acosta

Resident Physician
Houston Methodist Hospital
Houston, Texas

I am a very motivated Peruvian physician, currently on my 2nd year of Internal Medicine residency at Houston Methodist Hospital and with a great passion/interest/love for Endocrinology.

Ahmad Yehya

Endocrinology Fellow
Houston Methodist Hospital

A graduate of the American University of Beirut, Lebanon, Dr. Yehya completed his Internal Medicine Residency at the University of Kansas Medical Center. Dr. Yehya has a profound interest in metabolism and participated in various weight management programs and clinics throughout his Residency. Dr. Yehya will be working closely with the weight management program at Houston Methodist with special emphasis on weight loss medications, diet adjustment and exercise. Dr. Yehya is also particularly interested in the impact of lifestyle on diabetes. Dr. Yehya has specifically chosen to pursue his Endocrinology Fellowship at Houston Methodist as this will serve as a great template for launching a successful career in Endocrinology and he hopes to be able to develop weight management centers dedicated to focus on lifestyle changes for the community.

Laila Tabatabai

Assistant Professor of Clinical Medicine; Director, Houston Methodist Endocrinology Fellowship
Houston Methodist Hospital

Laila S. Tabatabai, M.D., is the Program Director of the Houston Methodist Endocrinology Fellowship Program. She is also the Director of the Houston Methodist Hospital Fracture Liaison Service (FLS) and Assistant Professor of Clinical Medicine in the Division of Endocrinology. She received her medical degree, with distinction in research, at Albany Medical College in Albany, New York. Her postdoctoral training included an internship and residency in internal medicine at the University of Maryland Medical Center in Baltimore and a fellowship in endocrinology at Johns Hopkins Hospital in Baltimore.