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NCT Number: NCT07268742

Free Vitamin D and Steroid Metabolism in Endocrine Disorders

This clinical study aims to gain a better understanding of how different forms of vitamin D are processed in the body in healthy individuals, pregnant women, and patients with various hormonal (endocrine) and kidney (renal) disorders. In the long term, this study may provide new insights that could how vitamin D is tested and interpreted in these groups.

Vitamin D has several important roles in the body, such as building strong bones and maintaining calcium balance in the blood. Most vitamin D in the blood circulation is attached/bound to a protein called "vitamin D binding protein" (VDBP), which makes it unavailable for the body to use. A much smaller portion circulates freely in the blood and this is called "free vitamin D". This free form can be directly used by the body.

When your doctor tests your vitamin D levels, this usually refers to total vitamin D (the sum of bound and free vitamin D). However, this total value may not give an accurate indication of your actual vitamin D status, since most of it (the bound part) cannot be used by the body. The purpose of this study is to examine whether "free vitamin D" is a better marker of vitamin D status and if the amount of free vitamin D differs between healthy people, pregnant women, and people with specific endocrine or kidney disorders.

Additionally, this study will look into vitamin D metabolism more detailed, and investigate what different forms of vitamin D exist, how the body processes these, and whether these forms may be related to certain endocrine or kidney conditions.

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Key information

Conditions

Vitamin D Vitamin D and Calcium Homeostasis

Age range

18 year and older

Sex eligibility

All sexes

Study type

Observational

Primary location

University Hospitals Leuven

Leuven, 3000, Belgium

Location status: Recruiting

Location contact

Nick Narinx, MD

CONTACT

[email protected]

+3216348516

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

  • General inclusion Criteria:
  • 18 years or above
  • General exclusion Criteria:
  • Below 18 years of age
  • Individuals incapable of providing informed consent
  • Cohort inclusion criteria
  • Obesity: BMI ≥ 25 kg/m2
  • Chronic Kidney Disease: ≥ CKD stage 3a (eGFR < 60 mL/min/1.73m2)
  • Pregnancy: in trimester 1 of pregnancy
  • Primary hyperparathyroidism: diagnosis at UZ Leuven and scheduled for parathyroidectomy at UZ Leuven
  • Complex calcium and phosphate disorders: diagnosis at UZ Leuven
  • Cohort exclusion criteria
  • Healthy controls: BMI below 18 kg/m² or above 25 kg/m², pregnancy, chronic kidney disease (independent of staging), primary hyperparathyroidism and vitamin D and/or calcium supplementation
  • Obesity: chronic kidney disease (independent of staging), pregnancy, primary hyperparathyroidism
  • Chronic Kidney Disease: BMI below 18 kg/m² or above 30 kg/m², pregnancy, primary hyperparathyroidism
  • Pregnancy: BMI below 18 kg/m² or above 30 kg/m², chronic kidney disease (independent of staging), primary hyperparathyroidism
  • Primary hyperparathyroidism: BMI below 18 kg/m² or above 30 kg/m², pregnancy, chronic kidney disease (independent of staging), secondary hyperparathyroidism

Treatment and study plan

Blood draw for the laboratory assessment

Other

Blood draw for the laboratory assessment

Primary outcomes

  1. Direct measurement of free 25-hydroxyvitamin D3 levels

    Time frame: - Baseline (all cohorts) - Baseline (trimester 1, week 1-12) , trimester 2 (week 13-27), trimester 3 (week 28-40) and 4-6 weeks after delivery (Pregnancy) - Baseline, perioperative and 4-8 weeks after parathyroidectomy (Primary Hyperparathyroidism)

    • Direct measurement of free 25-hydroxyvitamin D3, reported as concentration levels per cohort;
    • Reported at baseline
    • Reported as change versus healthy control group (all cohorts vs healthy control)
    • Reported as change within-cohort (Pregnancy and Primary Hyperparathyroidism).

Secondary outcomes

  1. Calculation of free 25-hydroxyvitamin D3 levels

    Time frame: - Baseline (all cohorts) - Baseline (trimester 1, week 1-12) , trimester 2 (week 13-27), trimester 3 (week 28-40) and 4-6 weeks after delivery (Pregnancy) - Baseline, perioperative and 4-8 weeks after parathyroidectomy (Primary Hyperparathyroidism)

    • Calculation of free 25-hydroxyvitamin D3, reported as concentration levels per cohort;
    • Reported at baseline
    • Reported as change versus healthy control group (all cohorts vs healthy control)
    • Reported as change within-cohort (Pregnancy and Primary Hyperparathyroidism).

  2. Correlation of measured and calculated free 25-hydroxyvitamin D3 levels

    Time frame: - Baseline (all cohorts) - Baseline (trimester 1, week 1-12) , trimester 2 (week 13-27), trimester 3 (week 28-40) and 4-6 weeks after delivery (Pregnancy) - Baseline, perioperative and 4-8 weeks after parathyroidectomy (Primary Hyperparathyroidism)

    Assessment of correlation between measured (Primary Outcome) and calculated (Secondary Outcome 1) free 25-hydroxyvitamin D3 levels

  3. Laboratory assessment of vitamin D metabolite profile

    Time frame: - Baseline (all cohorts) - Baseline (trimester 1, week 1-12) , trimester 2 (week 13-27), trimester 3 (week 28-40) and 4-6 weeks after delivery (Pregnancy) - Baseline, perioperative and 4-8 weeks after parathyroidectomy (Primary Hyperparathyroidism)

    Laboratory assessment of different vitamin D metabolites;

    • 25-hydroxyvitamin D3
    • 3-epi-hydroxyvitamin D3
    • 1(alpha).25-dihydroxyvitamin D3
    • 1(beta).25-dihydroxyvitamin D3
    • 3-epi-1.25-dihydroxyvitamin D3
    • 24.25-dihydroxyvitamin D3
    • 25-hydroxyvitamin D2
    • 1.25-dihydroxyvitamin D2

Study contacts

Contact information is provided by the study sponsor or research team.

Nick Narinx, MD

CONTACT

[email protected]

+3216348516

Sponsors and collaborators

Lead sponsor

Universitaire Ziekenhuizen KU Leuven

Other

Collaborators

  • KU Leuven

Registry information

Official study title

Free Fraction Vitamin D Measurements to Improve Understanding of Steroid Metabolism in Endocrine Disorders

Acronym: FREEDOM

Important dates

Study start
2024
Primary completion
2029
Study completion
2029
First posted
Dec 8, 2025
Registry last updated
Dec 8, 2025

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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