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 ¡À 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 (¡Ý 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 ¡Ü 0.01).
Lower 25-OHD concentration was observed in subjects with diabetes (19 ¡À 9 vs 14 ¡À 7 ng/mL, p < 0.01) and hypertension (20 ¡À 9 vs 17 ¡À 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 ¡Ü 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.