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Short-term Variability of Vitamin D-Related Biomarkers.

TitleShort-term Variability of Vitamin D-Related Biomarkers.
Publication TypeJournal Article
Year of Publication2016
AuthorsLutsey PL, Parrinello CM, Misialek JR, Hoofnagle AN, Henderson CM, Laha TJ, Michos ED, Eckfeldt JH
Secondary AuthorsSelvin E
JournalClin Chem
Volume62
Issue12
Pagination1647-1653
Date Published2016 Dec
ISSN1530-8561
KeywordsAged, Aged, 80 and over, Biomarkers, Female, Humans, Male, Middle Aged, Vitamin D
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 (CV), intraclass correlation coefficient (ICC), Spearman rank correlation coefficient (r), and percent reclassified.

RESULTS: The CV 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 CV, 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.

DOI10.1373/clinchem.2016.261461
Alternate JournalClin Chem
PubMed ID27694392
PubMed Central IDPMC5131784
Grant ListHHSN268201100009I / HL / NHLBI NIH HHS / United States
R01 HL103706 / HL / NHLBI NIH HHS / United States
HHSN268201100010C / HL / NHLBI NIH HHS / United States
HHSN268201100008C / HL / NHLBI NIH HHS / United States
R01 DK089174 / DK / NIDDK NIH HHS / United States
HHSN268201100007C / HL / NHLBI NIH HHS / United States
HHSN268201100011I / HL / NHLBI NIH HHS / United States
HHSN268201100011C / HL / NHLBI NIH HHS / United States
HHSN268201100006C / HL / NHLBI NIH HHS / United States
P30 DK035816 / DK / NIDDK NIH HHS / United States
HHSN268201100007I / HL / NHLBI NIH HHS / United States
HHSN268201100012C / HL / NHLBI NIH HHS / United States
T32 HL007028 / HL / NHLBI NIH HHS / United States
U24 CA160034 / CA / NCI NIH HHS / United States
HHSN268201100005G / HL / NHLBI NIH HHS / United States
HHSN268201100008I / HL / NHLBI NIH HHS / United States
HHSN268201100005I / HL / NHLBI NIH HHS / United States
K24 DK106414 / DK / NIDDK NIH HHS / United States
HHSN268201100009C / HL / NHLBI NIH HHS / United States
HHSN268201100005C / HL / NHLBI NIH HHS / United States