Preanalytical, analytical (DiaSorin LIAISON) and clinical variables potentially affecting the 25-OH Vitamin D estimation

Background: Vitamin D (25-OHD) physiological functions have been expanded beyond traditional bone health, increasing the importance of its estimation in Laboratory Medicine, which renders validation of available methods mandatory. Aims and methods: We evaluated some preanalytical and analytical aspects of 25-OHD determination and the effects of potentially confounding clinical variables by using the DiaSorin "LIAISON 25-OH Vitamin D TOTAL". Results: 25-OHD samples were extremely stable, at least in the short term, without requiring special transport or storage. Precision intervals (CV%) were: within run (7-11%) and total precision (8-11.5%). Mean (SD) recovery was 96 (2)%. The assay was linear on dilution. Comparison with radioimmunoassay (RIA) yielded acceptable correlation (Inter-rater agreement/kappa coefficient=0.94) and clinical equivalence in the interval from 6 to 55 ng/mL. The assay was evaluated on a general population (N=476, age: 60 +/- 14 years, 65 males). The status of 25-OHD resulted inversely related to parathyroid hormone levels (r=-0.21, p<0.001), and aging (r=-0.17, p<0.001), but not to sex. Levels of 25-OHD were found to be sufficient (>= 30 ng/mL) only in 54 samples (12%). Marked seasonal 25-OHD variations were observed in 13 subjects (p<0.05). Moreover, a marked seasonal fluctuation was seen in samples collected during the period of February 2010-October 2011 (p <= 0.01). Lower 25-OHD concentration was observed in subjects with diabetes (19 +/- 9 vs 14 +/- 7 ng/mL, p<0.01) and hypertension (20 +/- 9 vs 17 +/- 9 ng/mL, p<0.01). Moreover, 25-OHD inversely correlated with BMI (r=-0.25, p<0.001). Conversely, no difference in 25-OHD levels was observed between subjects due to smoking habits and dyslipidemia. In multiple logistic regression models, aging is the only significant independent risk factor for low 25-OHD levels (Odds ratio, 95% confidence intervals: 3.1, 1.3-7.3; p <= 0.01). Conclusions: Results confirm the LIAISON 25-OHD assay as a useful tool for 25-OHD estimation in the clinical practice. Lack of vitamin D is common among Italian adults, and appears associated with several cardiovascular risk factors. (C) 2012 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.