Accuracy Validation of 8 Equations to Estimate 24-Hour Sodium by Spot Urine in Young Adolescents.

BACKGROUND: Several formulas using spot urine have been developed to estimate 24-hour sodium excretion, but none of them have been validated in pediatrics. We aimed to evaluate the performance of 8 formulas-Kawasaki; Tanaka; International Cooperative Study on Salt, Other Factors, and Blood Pressure (INTERSALT1); INTERSALT without potassium (INTERSALT2); Mage; Whitton; Uechi simple-mean; and Uechi regression-in estimating 24-hour sodium excretion at both population and individual levels in Chinese young adolescents.

METHODS: This cross-sectional study consisted of 284 students aged 10-15 years from Hunan, China. Two spot urine and 24-hour urine samples were collected from each participant.

RESULTS: The median 24-hour urinary sodium excretion was 2,742 mg. The mean differences (95% confidence intervals) of 24-hour sodium excretion by the 8 equations were 1,613 (1,491 to 1,735) mg for Kawasaki, -12 (-97 to 73) mg for Tanaka, -214 (-319 to -110) mg for INTERSALT1, -289 (-394 to -185) mg for INTERSALT2, -615 (-730 to -500) mg for Mage, 1,082 (967 to 1,198) mg for Whitton, -479 (-610 to -348) mg for Uechi simple-mean, and -620 (-716 to -525) mg for Uechi regression. The Tanaka formula performed best in relative and absolute difference distributions, with 35.2% participants having relative differences within 10%, and 45.8% participants having absolute differences within 393 mg. The misclassification rates were all >50% except for the Tanaka formula (43.7%).

CONCLUSIONS: In our study, Tanaka could offer a plausible alternative of mean populational 24-hour sodium estimation for young adolescents. However, the results did not support the use of these equations in pediatrics at individual levels.