ArticleThe Journal of clinical endocrinology and metabolism2014
A comparison of measured and calculated free 25(OH) vitamin D levels in clinical populations.
Article in The Journal of clinical endocrinology and metabolism, 2014. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 110 papers.
What it found
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The abstract states no effect estimate the extractor could read, or names no intervention and outcome on the map, so this paper lights no cell and moves no belief. It is still indexed, cited and linked below.
The trial behind it
Trials whose registry record cites this paper, or whose number appears in the abstract. A trial that started after this paper was published is citing it as background, not reporting it.
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Who cites it
110 citing papers in PubMed, 179 citations in OpenAlex.
- Exploring associations between maternal vitamin D-binding protein, vitamin D, and offspring asthma/recurrent wheeze.The American journal of clinical nutrition · 2026Trial
- Total, Bioavailable, and Free 25(OH)D Relationship with Indices of Bone Health in Elderly: A Randomized Controlled Trial.The Journal of clinical endocrinology and metabolism · 2021Trial
- Effects of Supplemental Vitamin D on Bone Health Outcomes in Women and Men in the VITamin D and OmegA-3 TriaL (VITAL).Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research · 2020Trial
- Free vitamin D correlate better with bone mineral density and thoracolumbar junction osteoporotic vertebral fractures than serum vitamin D.BMC musculoskeletal disorders · 2020Trial
- Serum 25-hydroxyvitamin D in the VITamin D and OmegA-3 TriaL (VITAL): Clinical and demographic characteristics associated with baseline and change with randomized vitamin D treatment.Contemporary clinical trials · 2019Trial
- The effect of an exercise program in pregnancy on vitamin D status among healthy, pregnant Norwegian women: a randomized controlled trial.BMC pregnancy and childbirth · 2019Trial
- Association of free vitamin DAnnals of allergy, asthma & immunology : official publication of the American College of Allergy, Asthma, & Immunology · 2018Trial
- The relationship of Physical performance and Osteoporosis prevention with vitamin D in older African Americans (PODA).Contemporary clinical trials · 2018Trial
- Effects of Cholecalciferol vs Calcifediol on Total and Free 25-Hydroxyvitamin D and Parathyroid Hormone.The Journal of clinical endocrinology and metabolism · 2017Trial
- Vitamin D Metabolism Varies among Women in Different Reproductive States Consuming the Same Intakes of Vitamin D and Related Nutrients.The Journal of nutrition · 2016Trial
- Effects of High-Dose Vitamin D2 Versus D3 on Total and Free 25-Hydroxyvitamin D and Markers of Calcium Balance.The Journal of clinical endocrinology and metabolism · 2016Trial
- Vitamin D status of black and white Americans and changes in vitamin D metabolites after varied doses of vitamin D supplementation.The American journal of clinical nutrition · 2016Trial
- Effects of vitamin D binding protein phenotypes and vitamin D supplementation on serum total 25(OH)D and directly measured free 25(OH)D.European journal of endocrinology · 2016Trial
- Response of Vitamin D Concentration to Vitamin D3 Administration in Older Adults without Sun Exposure: A Randomized Double-Blind Trial.Journal of the American Geriatrics Society · 2016Trial
- Free 25-Hydroxyvitamin D Concentrations in Cystic Fibrosis.The American journal of the medical sciences · 2015Trial
- Free 25(OH)D and Calcium Absorption, PTH, and Markers of Bone Turnover.The Journal of clinical endocrinology and metabolism · 2015Trial
- Nutritional vitamin D supplementation in dialysis: a randomized trial.Clinical journal of the American Society of Nephrology : CJASN · 2015Trial
- Vitamin D as a cellular endocrine system: Tissue-specific microcircuits, immune reprogramming, and metabolic resistance.iScience · 2026Review
- Season-adjusted longitudinal changes in serum 25-hydroxyvitamin D during pegylated interferon add-on to ongoing tenofovir alafenamide therapy in chronic hepatitis B: a real-world cohort study.Frontiers in medicine · 2026Article
- Decrease in Vitamin D Binding Protein in Acute Fractures Does Not Affect Vitamin D Levels.Clinics in orthopedic surgery · 2025Article
50 more citing papers are in PubMed but not listed here.
Corrections and comments
PubMed lists nothing against this paper. Absence here is not a guarantee, only a check that was made.
Authors and funding
9 authors at 3 institutions in 1 country.
Funding
Abstract
objectiveOur goal was to compare direct quantitation of circulating free 25-hydroxyvitamin D (25(OH)D)levels to calculated free 25(OH)D levels and their relationships to intact PTH (iPTH), a biomarker of 25(OH)D effect, in humans with a range of clinical conditions. PATIENTS AND
methodsSerum samples and clinical data were collected from 155 people: 111 without cirrhosis or pregnancy (comparison group), 24 cirrhotic patients with albumin <2.9 g/dL, and 20 pregnant women (second and third trimester). Total 25(OH)D (LC/MS/MS), free 25(OH)D (immunoassay), vitamin D binding protein (DBP) (immunoassay), albumin, and iPTH (immunoassay) were measured.
resultsTotal 25(OH)D, DBP, and albumin were lowest in patients with cirrhosis, but measured free 25(OH)D was highest in this group (P < .001). DBP was highest in pregnant women (P < .001), but measured free 25(OH)D did not differ from the comparison group. Calculated free 25(OH)D was positively correlated with measured free 25(OH)D (P < .0001) but explained only 13% of the variability with calculated values higher than measured. African Americans had lower DBP than other ethnic populations within all clinical groups (P < .03), and differences between measured and calculated free 25(OH)D were greatest in African Americans (P < .001). Measured free 25(OH)D was correlated with total 25(OH)D (P < .0001; r(2) = 0.51), but calculated free 25(OH)D was not. Similarly, both measured free 25(OH)D (P < .02) and total 25(OH)D (P < .05) were correlated with iPTH, but calculated free 25(OH)D was not.
conclusionsCalculated free 25(OH)D levels varied considerably from direct measurements of free 25(OH)D with discrepancies greatest in the data for African Americans. Differences in DBP binding affinity likely contributed to estimation errors between the races. Directly measured free 25(OH)D concentrations were related to iPTH, but calculated estimates were not. Current algorithms to calculate free 25(OH)D may not be accurate. Further evaluation of directly measured free 25(OH)D levels to determine its role in research and clinical management of patients is needed.
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Registered trials
Read under generation 80e0d062 · epoch 390. Bibliography from PubMed, PubMed Central and OpenAlex; grants from NIH RePORTER; trial links from ClinicalTrials.gov; estimates, votes and beliefs from the OpenQuestion graph.