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

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.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".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, p0.001), and aging (r=-0.17, p0.001), 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 (p0.05). 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, p0.01) and hypertension (20±9 vs 17±9 ng/mL, p0.01). Moreover, 25-OHD inversely correlated with BMI (r=-0.25, p0.001). 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).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.