A New Approach Is Needed to Evaluate 24-Hour Urinary Sodium Excretion Using Spot Urines: A Validation Study in a Chinese Child Population.

Background Accurate assessments of sodium intake in children are important for the early prevention of cardiovascular disease. There is currently no accurate simple and feasible sodium intake approach for children. This study intends to validate the accuracy of 24-hour urinary sodium excretion (UNaV) estimation in children using 3 common formulas: the Kawasaki, INTERSALT (International Cooperative Study on Salt, Other Factors, and Blood Pressure), and Tanaka formulas. Methods and Results A hospital-based child population in China was enrolled in the study and completed 24-hour urine sample collection. Concentrations of sodium, potassium, and creatinine in 24-hour urine and spot urine samples were measured. Mean difference as well as absolute and relative differences and misclassification between estimation and measurement of UNaV with 3 commonly used formulas were compared and analyzed. A total of 129 participants aged 5 to 16 years were eligible for analysis. Mean measured UNaV was 2694.9 mg/day. Mean differences between estimated and measured UNaV by the Kawasaki, INTERSALT, and Tanaka formulas were 2367.6, 26.4, and 258.8 mg/day, respectively. Proportions of relative differences of over 40% for the Kawasaki, INTERSALT, and Tanaka formulas were 79.8%, 34.9%, and 38.5%, respectively. Misclassification rates were 73.1% for Kawasaki, 69.0% for INTERSALT, and 62.4% for Tanaka at the individual level. Conclusions The results from our study do not support estimation of UNaV for children by the Kawasaki, INTERSALT, and Tanaka formulas using single spot urine samples because of the potential risk for misclassification at the individual level.