Table 1.

Descriptive statistics and estimates of within-subject variability and agreement between serum concentrations of 25(OH)D measured at three time points (baseline, +1 y, and +5 y) over a 5-y period

AnalysisnValues
Season of blood draw*
    January-March7
    April-June6
    July-September11
    October-December5
Summary of 25(OH)D measures at:
    Baseline
        Mean (SD)2860.0 (14.6) nmol/L
        Median2860.2 nmol/L
        Range2833.7-99.6 nmol/L
    +1 y
        Mean (SD)2959.8 (15.9) nmol/L
        Median2959.5 nmol/L
        Range2928.6-94.2 nmol/L
    +5 y
        Mean (SD)2656.6 (16.2) nmol/L
        Median2655.1 nmol/L
        Range2624.1-98.2 nmol/L
Measures of agreement
    CV (95% CI)2914.9% (12.4-18.1%)
    ICC (95% CI)290.71 (0.63-0.88)
Spearman rank correlation coefficients (95% CI)
    Baseline vs. +1 y280.65 (0.37-0.82)
    +1 y vs +5 y260.61 (0.29-0.81)
    Baseline vs. +5 y250.53 (0.17-0.77)
    Baseline/+1 y average vs. +5 y250.65 (0.34-0.83)
  • *All participants had the serial blood draws during the same calendar month in each year. On average, samples were collected within a 13-d window (range, 2-26 d).