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

ABSTRACT

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.