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J Clin Endocrinol Metab. 2013 Jan;98(1):97-104. doi: 10.1210/jc.2012-2643. Epub 2012 Nov 8.

Variability and reproducibility of circulating vitamin D in a nationwide U.S. population.

Author information

1
Division of Cancer Epidemiology and Genetics, National Cancer Institute, 6120 Executive Boulevard, Bethesda, Maryland 20852, USA. majorjm@mail.nih.gov

Abstract

CONTEXT:

Most studies examining associations between circulating vitamin D and disease are based on a single measure of vitamin D, which may not reflect levels over time, particularly because vitamin D concentrations vary by season. Few studies evaluated how well multiple 25-hydroxyvitamin D [25(OH)D] measures track within the same individual over time.

OBJECTIVE:

This study examined variability and reproducibility of vitamin D by evaluating repeat measurements of plasma 25(OH)D concentrations while accounting for determinants of circulating concentrations including dietary supplement use and latitude of residence from a population of U.S. radiologic technologists.

DESIGN AND PARTICIPANTS:

We analyzed circulating 25(OH)D in blood samples taken from 538 men and women from a prospective, nationwide study at two time points within a 1-yr period, most measured in different seasons. Inter- and intra-individual variability, reliability coefficients, and measurement error were examined.

RESULTS:

The spearman rank correlation between two measurements of 25(OH)D concentrations was moderate (r = 0.75, P < 0.001) and did not vary significantly by participant characteristics including age, race, or latitude. The intraclass correlation coefficient was 0.72 (95% confidence interval = 0.68-0.76). The deattenuation factor of plasma 25(OH)D levels was 1.39, suggesting that a single measure of vitamin D on a continuous scale in regression analyses may result in attenuated relationships of about 40%.

CONCLUSION:

Our results suggest that a single blood sample obtained in spring or fall provides a reasonable average for 25(OH)D over a 1-yr period, but additional studies are needed to estimate variability and agreement in plasma 25(OH)D measurements over longer intervals and younger populations.

PMID:
23144464
PMCID:
PMC3537087
DOI:
10.1210/jc.2012-2643
[Indexed for MEDLINE]
Free PMC Article

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