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Geographical differences in 25(OH)D reference intervals.

Efsane Yavuz1, Mustafa Örkmez1, Mehmet Akif Bildirici2

  • 1Gaziantep University, Faculty of Medicine, Department of Medical Biochemistry, Gaziantep, Turkey.

The Journal of Steroid Biochemistry and Molecular Biology
|May 29, 2025
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Summary

Vitamin D deficiency is a global health issue. This study determined regional and seasonal reference ranges for 25(OH)D, finding levels often below recommended values.

Keywords:
25(OH)DDirect MethodEP28-A3cIndirect MethodReference Interval (RI)

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Area of Science:

  • Endocrinology
  • Public Health
  • Clinical Chemistry

Background:

  • Vitamin D deficiency is a significant global health concern.
  • Establishing accurate reference ranges for 25-hydroxyvitamin D (25(OH)D) is crucial for diagnosis and management.
  • Regional and seasonal variations, influenced by geography and diet, impact Vitamin D levels.

Purpose of the Study:

  • To determine the reference intervals for Vitamin D (25(OH)D) and related parameters (PTH, Ca, P, ALP).
  • To compare direct and indirect methods for establishing these reference ranges.
  • To investigate regional (Southeastern Anatolia vs. Black Sea) and seasonal (summer vs. winter) differences in Vitamin D levels.

Main Methods:

  • Utilized direct and indirect methods to calculate reference ranges for 25(OH)D.
  • Employed non-parametric methods (CLSI EP28-A3) for the direct method.
  • Applied data filtration and the Bhattacharya method for the indirect method.

Main Results:

  • Direct method 25(OH)D reference intervals varied by region and season (e.g., SE Anatolia: 8.03-29.44 ng/mL summer, 5.55-23.07 ng/mL winter).
  • Indirect method 25(OH)D reference intervals were 7.24-41.69 ng/mL (SE Anatolia) and 6.17-42.66 ng/mL (Black Sea).
  • Severe Vitamin D deficiency prevalence ranged from 7.6% to 30.5% across regions and seasons.

Conclusions:

  • Reference ranges for 25(OH)D show significant regional and seasonal variability.
  • The study highlights that 25(OH)D levels in the studied populations were frequently below recommended ranges.
  • Accurate, region-specific reference intervals are essential for addressing Vitamin D deficiency.