Study of the Impact of Phosphate Supplementation on FGF23 Concentrations in Patients With Hypophosphatemia (PHOSPHO-23)

September 17, 2026 updated by: University Hospital, Clermont-Ferrand

Fibroblast growth factor 23 (FGF23) is the principal hormone regulating serum phosphate homeostasis. Secreted by osteocytes, it promotes renal phosphate excretion and suppresses the synthesis of 1,25-dihydroxyvitamin D. Measurement of FGF23 has become a key tool in the evaluation of hypophosphatemia, allowing distinction between FGF23-dependent forms (such as X-linked hypophosphatemic rickets, tumor-induced osteomalacia, and intravenous iron-induced hypophosphatemia) and FGF23-independent forms (including renal, gastrointestinal, nutritional, or drug-related causes).

In healthy adults, several studies have demonstrated that FGF23 levels vary according to phosphate intake, decreasing during dietary restriction and increasing following phosphate loading. In hypophosphatemic conditions, however, available data are limited to X-linked hypophosphatemic rickets, where prolonged supplementation with phosphate and calcitriol leads to increased FGF23 levels, consistent with the underlying pathophysiology.

Based on these observations, it is currently recommended, as a precaution, to measure FGF23 at least 15 days after discontinuation of phosphate supplementation in order to avoid transient elevations that may confound interpretation. In practice, however, this recommendation is difficult to implement, as most patients are already receiving phosphate supplementation at the time of evaluation.

To date, no study has specifically assessed the effect of phosphate supplementation in patients with FGF23-independent hypophosphatemia, a condition characterized by appropriately low FGF23 levels. It therefore remains unclear whether supplementation could induce a transient rise in circulating FGF23, potentially leading to misclassification as FGF23-dependent hypophosphatemia (FGF23 > 95 ng/L).

This uncertainty provides a strong rationale for conducting the present study.

Study Overview

Status

Recruiting

Conditions

Intervention / Treatment

Study Type

Interventional

Enrollment (Estimated)

60

Phase

  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Locations

  • France
      • Clermont-Ferrand, France
      • Clermont-Ferrand, France
      • Clermont-Ferrand, France

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Adult
  • Older Adult

Accepts Healthy Volunteers

No

Description

Inclusion Criteria:

  • Patients hospitalized in adult intensive care, oncology, or rheumatology
  • Hypophosphatemia < 0.8 mmol/L
  • Clinical indication for phosphate supplementation

Exclusion Criteria:

  • Chronic kidney disease, stage ≥ 3 (eGFR < 60 mL/min/1.73 m²)
  • Treatment with Ferinject® within the past year
  • Sepsis
  • Current treatment with active vitamin D
  • Pregnancy or breastfeeding
  • Inability to perform blood draws due to insufficient venous access
  • Weight < 35 kg (for intensive care patients only)
  • Hypercalcemia > 2.6 mmol/L

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Other
  • Allocation: N/A
  • Interventional Model: Single Group Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Other: Patients hospitalized in adult intensive care, oncology, or rheumatology
Biological: Blood sample
Collection of one EDTA tube for FGF23 measurement and one heparin tube for phosphorus measurement

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Impact of phosphate supplementation on plasma FGF23 levels in acquired FGF23-independent hypophosphatemia
Time Frame: Up to 21 days

To determine whether phosphate supplementation modifies plasma FGF23 concentrations in patients with acquired FGF23-independent hypophosphatemia by studying changes in FGF23 concentrations following phosphate supplementation.

The primary objective will be studied separately in two groups: first, in intensive care patients, and second, in oncology/rheumatology patients.
Up to 21 days

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

University Hospital, Clermont-Ferrand

Investigators

  • Study Chair: Damien BOUVIER, CHU Clermont-Ferrand service de biochimie

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

June 13, 2026

Primary Completion (Estimated)

May 1, 2027

Study Completion (Estimated)

September 1, 2027

Study Registration Dates

First Submitted

September 11, 2026

First Submitted That Met QC Criteria

September 17, 2026

First Posted (Actual)

September 18, 2026

Study Record Updates

Last Update Posted (Actual)

September 18, 2026

Last Update Submitted That Met QC Criteria

September 17, 2026

Last Verified

September 1, 2026

More Information

Terms related to this study

Additional Relevant MeSH Terms

Other Study ID Numbers

  • RBHP 2025 BOUVIER

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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