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Measurement of the Free Fraction of 25-hydroxyvitamin D in Serum

The safety and scientific validity of this study is the responsibility of the study sponsor and investigators. Listing a study does not mean it has been evaluated by the U.S. Federal Government. Read our disclaimer for details. Identifier: NCT01771380
Recruitment Status : Completed
First Posted : January 18, 2013
Last Update Posted : September 22, 2015
Information provided by (Responsible Party):
University of Tromso

Brief Summary:
In the circulation 25-hydroxyvitaminD (25(OH)D) is bound to the vitamin D binding protein (DBP) and albumin. According to the free hormone hypothesis, it is, however, the free fraction that is biologically active. Polymorphisms in DBP are related to the serum level of 25(OH)D. As these polymorphisms may also affect the binding affinities for 25(OH)D, the total serum 25(OH)D may not necessary reflect the free fraction. To test this hypothesis, we will calculate the free fraction of 25(OH)D by correction for DBP and albumin content, and also measure free 25(OH)D from equilibrium dialysis and ultra filtration. Furthermore, we will relate total serum 25(OH)D as well as the free and biologically active (free- albumin-bound) 25(OH)D to the well established vitamin D effect marker serum parathyroid hormone as well as to the RNA expression in peripheral blood to evaluate the biological importance of the free versus the total fraction of 25(OH)D. We will invite 300 subjects from an ongoing vitamin D supplementation study to participate in the study which will be one visit only and include collection of blood samples.

Condition or disease
Impaired Glucose Tolerance

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Study Type : Observational
Actual Enrollment : 78 participants
Observational Model: Cohort
Time Perspective: Cross-Sectional
Official Title: Measurement of the Free Fraction of 25-hydroxyvitamin D in Serum
Study Start Date : February 2013
Actual Primary Completion Date : June 2015
Actual Study Completion Date : August 2015

Subjects with impaired glucose tolerance

Primary Outcome Measures :
  1. Free fraction of 25(OH)D [ Time Frame: 1 day ]

Secondary Outcome Measures :
  1. DBP polymorphisms [ Time Frame: 1 day ]

Other Outcome Measures:
  1. RNA expression in peripheral blood [ Time Frame: 1 day ]

Information from the National Library of Medicine

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Ages Eligible for Study:   25 Years to 85 Years   (Adult, Older Adult)
Sexes Eligible for Study:   All
Accepts Healthy Volunteers:   Yes
Sampling Method:   Non-Probability Sample
Study Population
Subjects with known impaired glucose tolerance

Inclusion Criteria:

  • Impaired glucose tolerance
  • living in the Tromsø area

Exclusion Criteria

  • pregnancy
  • serious illness

Information from the National Library of Medicine

To learn more about this study, you or your doctor may contact the study research staff using the contact information provided by the sponsor.

Please refer to this study by its identifier (NCT number): NCT01771380

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University of Tromsø
Tromsø, Norway, 9037
Sponsors and Collaborators
University of Tromso
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Responsible Party: University of Tromso Identifier: NCT01771380    
Other Study ID Numbers: Tromsø-Endo-2013-1
First Posted: January 18, 2013    Key Record Dates
Last Update Posted: September 22, 2015
Last Verified: September 2015
Additional relevant MeSH terms:
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Glucose Intolerance
Glucose Metabolism Disorders
Metabolic Diseases