Case Report: Unexplained Mild Hypophosphatemia and Very High Serum FGF23 Concentrations

Ariadne Bosman, Danielle M.A. Ratsma, Bram C.J. van der Eerden, M. Carola Zillikens*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

48 Downloads (Pure)

Abstract

Fibroblast growth factor (FGF)23 is one of the major regulators of phosphate homeostasis. Hypophosphatemia can lead to muscle weakness, fatigue, and osteomalacia. In the setting of hypophosphatemia, serum FGF23 can be measured to differentiate between FGF23-mediated and non-FGF23-mediated renal phosphate wasting. C-terminal FGF23 (cFGF23) assays detect both cFGF23 and intact FGF23 (iFGF23). Circulating FGF23 is regulated by 1.25-dihydroxy-vitamin D, parathyroid hormone (PTH), serum phosphate, and serum calcium but also by, for example, iron status, inflammation, erythropoietin, and hypoxia-inducible-factor-1-α. We present the case of a 48-year-old woman with unexplained mild hypophosphatemia, very high cFGF23, and normal iFGF23. The patient proved to have an iron deficiency. Iron deficiency alters the iFGF23-to-cFGF23 ratio. After initiation of iron treatment, cFGF23 strongly decreased. This case report illustrates the limitation of cFGF23 assays and urges clinicians to be aware that cFGF23 concentrations do not necessarily reflect iFGF23 concentrations and that alternative causes for its elevation should be considered (eg, iron deficiency).

Original languageEnglish
Article numbere10790
JournalJBMR Plus
Volume7
Issue number10
Early online date9 Aug 2023
DOIs
Publication statusPublished - Oct 2023

Bibliographical note

Funding Information:
AB and DMAR are supported by a grant from Health~Holland (PhosphoNorm; LSHM18029).

Publisher Copyright:
© 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Fingerprint

Dive into the research topics of 'Case Report: Unexplained Mild Hypophosphatemia and Very High Serum FGF23 Concentrations'. Together they form a unique fingerprint.

Cite this