Accuracy of Capillary Blood for Assessing Vitamin A Nutritional Status Among Children Under 7 Years of Age: A Multicenter Study.

Vitamin A deficiency remains a major public health problem worldwide, particularly among young children. Capillary blood has the potential for application in vitamin A assessment. The aim of this study is to validate the accuracy of capillary blood for assessing vitamin A nutritional status among young children. Venous and capillary blood samples were simultaneously collected from 1366 healthy children under 7 years of age across 12 regions in China. Retinol was measured using high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS). The agreement was assessed with Bland-Altman plot, Kappa, and prevalence-adjusted and bias-adjusted kappa (PABAK) values. The sensitivity and specificity were evaluated using the ROC curve method. Venous and capillary retinol levels showed significant differences but were highly correlated with r of 0.93. Ordinary least squares regression was used to characterize (β = 0.913) and correct the systematic bias in capillary data (compared to paired venous). Thereafter, Bland-Altman analysis demonstrated that the mean bias of corrected capillary retinol compared to venous retinol was 0.01 (95%CI: -0.24, 0.25) μmol/L with no significant difference (p ＞ 0.05). Corrected capillary retinol showed excellent performance for estimating vitamin A status when compared to venous retinol, with Kappa of 0.77-0.83, PABAK of 0.80-0.96, sensitivity of 0.86-0.91 and specificity of 0.87-0.98. Capillary HPLC-MS/MS method is therefore adequate for assessing vitamin A status of young children after correction for systematic bias.