[Standardization of clinical application of mass spectrometry method for measurement of vitamin D in capillary blood of children: a multicenter study].

Objective: To establish the norms and clinical application standards of mass spectrometry method to measure vitamin D in capillary blood. Methods: Following the "Province-City-Hospital" sampling procedure, a cross-sectional sample of 1 655 healthy children under 7 years of age were recruited from 12 provinces, autonomous regions, or municipalities in China from November 2020 to December 2021. Both venous and capillary blood samples from the same individual were collected, for which serum 25(OH)D levels were measured by high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS) method. Pearson correlation analysis and linear regression analysis were used to detect the correlation and determine a correction algorithm. The agreement was analyzed using Bland-Altman plot and Kappa statistic. The sensitivity and specificity were evaluated using receiver operating characteristic (ROC) curve method. Results: Venous and capillary 25(OH)D levels of 1 655 healthy children under 7 years of age were 74.25 (59.50, 92.00) and 68.75 (54.44, 86.25) nmol/L, respectively, showed a significant difference(Z=22.14, P<0.001) as well as a highly significant correlation between venous and capillary 25(OH)D levels(r=0.95, P<0.001). Linear regression analysis was then performed to determine the correction algorithm: lg(corrected capillary 25(OH)D)=0.13+0.95×lg(capillary 25(OH)D)(R2=0.90,P<0.001). The deviation between venous and corrected capillary 25(OH)D levels was (0.50±17.50) nmol/L, a difference value that did not reach statistical significance (P>0.05). The cut-off values of capillary blood 25(OH)D values 30.00, 50.00, 75.00 nmol/L corresponding to venous blood 25(OH)D values were 26.59, 45.56, and 69.84 nmol/L, respectively. Good consistency was observed between venous and corrected capillary 25(OH)D levels in clinical diagnosis (Kappa value 0.68-0.81). Corrected capillary 25(OH)D showed a high clinically predictive value (area under curve 0.97-0.99,sensitivity 0.72-0.92,specificity 0.89-0.99). Conclusion: The standardized capillary HPLC-MS/MS method can be used to detect 25(OH)D levels in children clinically.

[Analysis of vitamin D status among children under 7 years of age in some regions of China].

Objective: To explore current vitamin D status and influential factors of vitamin D deficiency and insufficiency among children under 7 years of age in 11 provinces, autonomous regions or municipalities of China. Methods: According to the "province-city-hospital" sampling technical route, a total of 1 531 healthy children under 7 years of age were sampled from 11 provinces, autonomous regions or municipalities in China by the cluster random sampling method from November 2020 to November 2021. The demographic information, family conditions, behavior and living habits and feeding behaviors were collected using unified questionnaire. Serum 25-hydroxyvitamin D(25(OH)D) levels were measured by liquid chromatography-tandem mass spectrometry. Serum 25(OH)D<30 nmol/L was considered deficient and 30-50 nmol/L was considered insufficient. With 25(OH)D≤50 nmol/L as the dependent variable, multivariate Logistic regression was applied to analyze the association between vitamin D deficiency and insufficiency and potential influential factors. Results: The prevalence of vitamin D deficiency and insufficiency among children under 7 years of age in 11 provinces, autonomous regions or municipalities of China was 14.0% (215/1 531), 3.8% (25/664) and 21.9% (190/867) in 0-<3 and 3-<7 of age years, respectively. Compared to children aged 0-<3 years, children aged 3-<7 years had a 2.6-fold increased risk of vitamin D deficiency and insufficiency (OR=3.60, 95%CI 1.93-6.72, P<0.001). Frequent sunlight exposure (OR=0.46, 95%CI 0.29-0.73, P=0.001), vitamin D supplementation (sometimes, OR=0.33, 95%CI 0.21-0.51, P<0.001; daily, OR=0.20, 95%CI 0.11-0.36, P<0.001) and infant formula intake(4-7 times per weeks, OR=0.43, 95%CI 0.28-0.68, P<0.001) were protective factors for vitamin D deficiency and insufficiency. Conclusion: Vitamin D deficiency and insufficiency are common among children under 7 years of age in 11 provinces, autonomous regions or municipalities of China, which is affected by age, sunlight exposure, vitamin D supplementation and infant formula intake.