Urinary iodine excretion (UIE) estimated by iodine/creatinine ratio from spot urine in Chinese school‐age children

Abstract

To assess the validity of urinary iodine excretion (UIE) estimated by urinary iodine/creatinine ratio (UI/Cr) from spot urines in Chinese school-age children. A cross-sectional survey was performed in which twice-repeated collections of 24-h urine and spot urine samples were obtained within one month. Urinary iodine concentration (UIC), urinary creatinine concentration (UCr), urine volume (Uvol) of spot and 24-h urine samples were measured. Measured 24-h UIE was calculated from 24-h UIC multiplied by 24-h Uvol, while the estimated 24-h UIE was calculated from spot UI/Cr multiplied by 24-h urinary creatinine excretion (24-h UCrE). No significant difference was observed in 24-h Uvol between two repeated collections (P=0.70), while spot UIC, 24-h UIC, spot UI/Cr and measured 24-h UIE were significantly different (Pr=0.57, Pr=0.63, Pr=0.83, Pr=0.60, Pr=0.72, Pr=0.89, P<0.001) were also correlated with measured 24-h UIE. The Bland-Altman results indicated 95% of subjects were expected to locate within the limits of agreement (LOA), but showed an underestimation of the urinary iodine excretion by the estimated 24-h UIE. In addition, moderate to good agreement was found for the estimated and measured 24-h UIE, with kappa values of 0.55 and 0.66. Estimated 24-h UIE by UI/Cr ratio from spot urine could represent a valid and reliable alternative for measured 24-h UIE in estimating iodine excretion in children.