Serum vitamin d reference range
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Serum Vitamin D Reference Range
Introduction to Serum Vitamin D Levels
Vitamin D is crucial for maintaining bone health and supporting various bodily functions. The primary marker for assessing vitamin D status is serum 25-hydroxyvitamin D [25(OH)D]. Establishing accurate reference ranges for serum 25(OH)D is essential for diagnosing deficiencies and guiding supplementation.
Dietary Reference Values for Vitamin D
Recent studies have utilized individual participant data (IPD) meta-analyses to derive more precise dietary reference values (DRV) for vitamin D. These analyses suggest that to maintain serum 25(OH)D concentrations of ≥25 nmol/L and ≥30 nmol/L, an intake of 6 µg/day and 12 µg/day, respectively, is required. To maintain higher concentrations of ≥50 nmol/L, the required intakes are significantly higher, ranging from 17.0 to 92.3 µg/day depending on the model used .
Vitamin D Supplementation Guidelines
Guidelines for vitamin D supplementation vary based on the desired health outcomes. For bone health, a target serum 25(OH)D concentration of 50 nmol/L (20 ng/mL) is recommended, with daily vitamin D doses of 400-800 IU. For broader health benefits, including the pleiotropic effects of vitamin D, a higher target of 75 nmol/L (30 ng/mL) is suggested, with doses ranging from 400 to 2000 IU/day, adjusted for factors such as age, body weight, and disease status .
Reference Intervals for Vitamin D Metabolites
The measurement of serum 24,25-dihydroxyvitamin D [24,25(OH)2D], a product of 25(OH)D catabolism, can provide additional insights into vitamin D status. A study established reference intervals for the 25(OH)D:24,25(OH)2D ratio in healthy individuals, finding a range of 7-23. A concentration of 24,25(OH)2D >4.2 nmol/L was identified as indicative of sufficient 25(OH)D status .
Standard Reference Materials for Vitamin D
The National Institute of Standards and Technology (NIST) has developed Standard Reference Materials (SRM) for vitamin D metabolites in human serum. These SRMs provide certified values for 25(OH)D2, 25(OH)D3, and 3-epi-25(OH)D3, ensuring accurate and reliable measurements across different laboratories 45.
Vitamin D Intake and Serum Levels
Meta-regression analyses have explored the relationship between vitamin D intake and serum 25(OH)D levels. These studies indicate that to achieve a serum 25(OH)D concentration of 50 nmol/L, an intake of approximately 930 IU/day may be necessary to account for inter-individual variability .
Impact of Vitamin D on Parathyroid Hormone (iPTH) Levels
Vitamin D status significantly impacts the reference intervals for intact parathyroid hormone (iPTH). In populations with prevalent vitamin D insufficiency, the upper reference limit for iPTH is higher. For individuals with sufficient vitamin D levels, the iPTH reference interval is narrower, highlighting the importance of considering vitamin D status in clinical assessments .
Regional and Demographic Variations
Reference intervals for serum 25(OH)D can vary based on ethnicity, age, and region. For instance, in Iranian children and adolescents, the reference intervals for 25(OH)D ranged from 11.45 to 48.40 ng/mL in boys and 9.51 to 47.69 ng/mL in girls, with significant differences observed between urban and rural residents .
Conclusion
Establishing accurate reference ranges for serum vitamin D is critical for diagnosing deficiencies and guiding supplementation. These ranges can vary based on dietary intake, demographic factors, and regional differences. Ongoing research and standardized reference materials are essential for ensuring reliable assessments of vitamin D status.
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