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

ObjectiveTo assess the validity of urinary iodine excretion (UIE) estimated by urinary iodine/creatinine ratio (UI/Cr) from spot urines in Chinese school-age children. DesignA cross-sectional survey was performed in which twice-repeated collections of 24-h urine, and spot urine samples were obtained within 1 month. MeasurementsUrinary 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). ResultsNo significant difference was observed in 24-h Uvol between two repeated collections (P = 070), while spot UIC, 24-h UIC, spot UI/Cr and measured 24-h UIE were significantly different (P < 005). The estimated 24-h UIE was 247 (136-431) g/day in the first collection, lower than the measured 24-h UIE of 329 (183-536) g/day (P < 0001), while no significant difference was observed (P = 030) in the second sampling as the estimated 24-h UIE was 355 (168-624) g/day and the measured 24-h UIE 350 (181-615) g/day. The spot UIC (r = 057, P < 0001), spot UI/Cr (r = 063, P < 0001) and the estimated 24-h UIE (r = 083, P < 0001) were strongly correlated with the measured 24-h UIE in the first collection. Likewise, in the second sampling, spot UIC (r = 060, P < 0001), spot UI/Cr (r = 072, P < 0001) and the estimated 24-h UIE (r = 089, P < 0001) 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 055 and 066. ConclusionsEstimated 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.