Biological Variability of Serum 25-Hydroxyvitamin D and Other Biomarkers in Healthy Subjects

Background: When monitoring serum levels of 25-hydroxyvitamin D (25-HD), it may be important to assess the significance of variations in the concentrations in the same individual. Data on biological variation is helpful in assessing and estimating critical differences to detect significant changes. The purpose of this article is to evaluate the biological variations of serum 25-HD and other biomarkers (ie, calcium, phosphorus, and parathormone [i-PTH]) in healthy subjects. Methods: We analyzed blood samples from 11 apparently healthy laboratory workers (6 women and 5 men; mean [SD] age, 46 [5.1] years; range, 39-55); the samples were obtained once a week for 12 weeks. All samples were analyzed in a single run in duplicate. Serum 25-HD concentrations were determined with the chemiluminescent analyzer LIAISON. For the same samples, we also determined the levels of parathormone (i-PTH), calcium (Ca), and phosphorus (P). The intraindividual (CVI) and interindividual (CVG) biological variation reference change value (RCV) and the index of individuality (II) were calculated.