Validation of 4 Estimating Methods to Evaluate 24-hour Urinary Sodium Excretion for Young Adults in China by Different Seasons

Background: 24-hour urine sample collection is regarded as the gold standard for sodium intake evaluation, but the implementation can be difficult. To validate and evaluate the accuracy and feasibility of estimating sodium intake by four methods of Kawasaki, INTERSALT, Tanaka and Sun’s equations. Methods: 274 healthy volunteers aged 18-25y were enrolled in this study. 24-hour urine samples as well as timed (morning, afternoon, evening and overnight) urine samples were randomly collected. The sodium intake were estimated by 4 published equations—Kawasaki, INTERSALT Tanaka and Sun’s. The consistencies between estimated sodium intake and real measured values of 24-hour urine sodium excretion were compared by Bland-Altman plots in each of the methods. Taking the variability of sodium excretion in different seasons into account, this study was conducted separately in summer (end of June 2017) and fall (end of November 2017). Results: The 24-h urinary sodium analysis result indicated an average daily sodium intake of 3043.0±1223.3mg in summer, and 3563.7±1370.0mg in the fall. Compared with autumn, the average daily reduction in sodium was about 520.7 mg. From the group level, the mean bias (estimated value - measured value) of the INTERSALT method with morning specimens (-39.7 mg ) was the smallest in summer. The mean bias of Tanaka method for prediction of morning specimens (-149.8 mg ) was the smallest in autumn. For the individual level, the correlation between 24-hour urinary sodium excretion and Sun’s methods was low, with a correlation coefficient of 0.406 in summer and 0.476 in the fall. Correlation coefficients between Kawasaki, INTERSALT, Tanaka methods and 24-hour urinary sodium excretion, respectively was in the range of 0.48-0.64. The correlation coefficient of Kawasaki method was the highest in summer (0.612) while that of Tanaka method with the afternoon specimens was the highest in the autumn (0.635). Conclusions: Estimation of sodium intakes among young adults using the 4 methods have varying degrees of bias and volatility in different times and seasons.