Agreement between measurement of 25-hydroxyvitamin D3 in dried blood spot samples and serum in a Chinese population in the Netherlands.

Blood for determining 25-hydroxyvitamin D3 [25(OH)D3] is usually obtained through venipuncture although, as an alternative for serum, dried blood spot (DBS) can be considered. The aim of this proof-of-concept study was to investigate levels of agreement between measurements of 25(OH)D3 obtained with DBS compared with serum. 301 Chinese participants were included who completed 25(OH)D3 measurement from DBS and from simultaneously collected blood samples obtained by venipuncture. Measurements of both DBS and serum 25(OH)D3 were performed using liquid chromatography followed by tandem mass spectrometry. Agreement between the two methods was assessed with Passing and Bablok regression analysis and Bland-Altman plot. Measurements showed a good correlation (Pearson's correlation coefficient r = 0.929, P < 0.001) between the two methods. After recalculating for a 13% difference, a regression equation of DBS 25(OH)D3 = -1.91 + 1.00 serum 25(OH)D3 was found in Passing and Bablok regression analysis. Bland-Altman analysis showed a fixed bias of 1.7 nmol/L; upper and lower limit of agreement was 24.1 nmol/L and -20.7 nmol/L, respectively. Sensitivity of recalculated DBS for 25(OH)D3 concentrations <30 and <50 nmol/L was 87.8% and 91.1%, respectively, and specificity was 89.2% and 83.1%, respectively. In conclusion, a good agreement was found between the measurement of 25(OH)D3 obtained with DBS compared with serum. DBS may possibly be used in a future screening program, but it is less suitable for individualized vitamin D status assessment.

Vitamin D status in the Chinese population in the Netherlands: The DRAGON study.

INTRODUCTION: Vitamin D is essential for bone health since it stimulates the intestinal absorption of calcium and phosphorus from the gut, both necessary for bone mineralization. However, vitamin D deficiency is highly prevalent among several non-Western immigrant populations in the Netherlands. To date, there are no data available of the vitamin D status in the Chinese population residing in the Netherlands. Therefore, an observational study was performed to determine 25-hydroxyvitamin D (25(OH)D) concentrations and to assess potential determinants of low vitamin D status. METHODS: Subjects, aged 18 years and older, with a Chinese background and residing in the Netherlands were invited to participate in the study. A questionnaire was used to assess general characteristics and lifestyle habits. Fasting blood samples were obtained in March 2014 to measure serum 25(OH)D concentration, and analysed by liquid chromatography tandem mass spectrometry. RESULTS: 418 subjects participated in the study, 104 men and 314 women. The mean age for both men and women was 56 years. Serum 25(OH)D concentration <50nmol/L was more prevalent in men than in women (67.9% and 53.1%, respectively; p=0.008). The percentage of serum 25(OH)D concentration<25nmol/L in men and women was 5.8% and 10.9%, respectively. Multiple logistic regression analysis, adjusted for age and gender, revealed that non-use of vitamin D supplements and fewer days per week of physical activity were significant predictors of serum 25(OH)D levels below 50nmol/L. CONCLUSIONS: Within the Chinese population living in the Netherlands, serum 25(OH)D concentration was below 50nmol/L in 68% of men and 53% of women. Use of vitamin D supplements by Chinese people in the Netherlands was highly protective against low 25(OH)D levels.