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Clin Chem. 2016 Dec;62(12):1647-1653. Epub 2016 Sep 30.

Short-term Variability of Vitamin D-Related Biomarkers.

Author information

1
Division of Epidemiology and Community Health, University of Minnesota School of Public Health, Minneapolis, MN; Lutsey@umn.edu.
2
Department of Epidemiology & Population Health, Albert Einstein College of Medicine, Bronx, NY.
3
Division of Epidemiology and Community Health, University of Minnesota School of Public Health, Minneapolis, MN.
4
Department of Laboratory Medicine, University of Washington, Seattle, WA.
5
Division of Cardiology, Johns Hopkins University, Baltimore, MD.
6
Department of Epidemiology and the Welch Center for Prevention, Epidemiology and Clinical Research, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD.
7
Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis, MN.

Abstract

BACKGROUND:

Quantifying the variability of biomarkers is important, as high within-person variability can lead to misclassification of individuals. Short-term variability of important markers of vitamin D metabolism is relatively unknown.

METHODS:

A repeatability study was conducted in 160 Atherosclerosis Risk in Communities study participants (60% female, 28% black, mean age 76 years). Fasting serum was drawn at 2 time points, a median of 6 (range 3-13) weeks apart. Vitamin D binding protein (VDBP) and 25-hydroxyvitamin D [25(OH)D] were measured by LC-MS, fibroblast growth factor (FGF23) and parathyroid hormone (PTH) by enzyme-linked immunoassay, and calcium and phosphorus by Roche Cobas 6000. Free and bioavailable 25(OH)D were calculated. We calculated the within-person CV (CVW), intraclass correlation coefficient (ICC), Spearman rank correlation coefficient (r), and percent reclassified.

RESULTS:

The CVW was lowest for calcium (2.0%), albumin (3.6%), 25(OH)D (6.9%), VDBP (7.0%) and phosphorus (7.6%); intermediate for free 25(OH)D (9.0%) and bioavailable 25(OH)D (9.9%); and highest for PTH (16.7%) and FGF23 (17.8%). Reclassification was highest for PTH, VDBP, and phosphorus (all 7.5%). The ICC and r were highest (≥0.80) for 25(OH)D, free 25(OH)D, bioavailable 25(OH)D and PTH, but somewhat lower (approximately 0.60-0.75) for the other biomarkers.

CONCLUSIONS:

Six-week short-term variability, as assessed by CVW, was quite low for VDBP, calcium and phosphorus, but fairly high for FGF23 and PTH. As such, multiple measurements of FGF23 and PTH may be needed to minimize misclassification. These results provide insight into the extent of potential misclassification of vitamin D markers in research and clinical settings.

PMID:
27694392
PMCID:
PMC5131784
DOI:
10.1373/clinchem.2016.261461
[Indexed for MEDLINE]
Free PMC Article

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