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Reference intervals for measured and calculated free 25-hydroxyvitamin D in normal pregnancy
Oleg Tsuprykov1, Claudia Buse2, Roman Skoblo2
1Institute of Nutritional Sciences, University of Potsdam, Potsdam, Germany; Institute for Laboratory Medicine, IFLB, Berlin, Germany.
The Journal of Steroid Biochemistry and Molecular Biology
|March 24, 2018
Summary
Free 25-hydroxyvitamin D (25(OH)D) better reflects vitamin D status in pregnancy than total 25(OH)D. Free 25(OH)D levels decrease in the third trimester and correlate with calcium and bone health markers.
Area of Science:
- Endocrinology
- Biochemistry
- Maternal Health
Background:
- Vitamin D status is crucial during pregnancy, but total 25-hydroxyvitamin D (25(OH)D) levels can be influenced by binding proteins.
- Vitamin D-binding protein (DBP) increases during pregnancy, affecting total 25(OH)D measurements.
- Free 25(OH)D is less dependent on DBP, potentially offering a more accurate reflection of vitamin D status.
Purpose of the Study:
- To compare the utility of free 25(OH)D versus total 25(OH)D in assessing vitamin D status during pregnancy.
- To investigate the changes in free and total 25(OH)D levels across pregnancy trimesters.
- To examine the correlations between 25(OH)D isoforms and key biomarkers of calcium and bone metabolism.
Main Methods:
- Study involved 368 healthy pregnant Caucasian women in Northeastern Germany.
- Free 25(OH)D was measured directly (ELISA) and calculated using total 25(OH)D, DBP, and albumin.
- Correlations with serum calcium and bone-specific alkaline phosphatase (BSAP) were analyzed.
Main Results:
- Free 25(OH)D decreased significantly in the third trimester compared to the first, while total 25(OH)D did not.
- Free 25(OH)D showed significant positive correlations with serum calcium.
- Both measured and calculated free 25(OH)D exhibited stronger negative correlations with BSAP than total 25(OH)D.
Conclusions:
- Free 25(OH)D, whether measured or calculated, is a more reliable indicator of vitamin D status in pregnancy than total 25(OH)D.
- Pregnancy trimester-specific reference intervals for free 25(OH)D and DBP were established.
- Free 25(OH)D assessment may replace total 25(OH)D testing for monitoring vitamin D status in pregnant women.
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