Validity of five formulas in estimating 24-h urinary sodium via spot urine sampling in hypertensive patients living in Northeast China

Objective: The objective was to evaluate the accuracy of five formulas -- the Kawasaki, Tanaka, INTERSALT, Mage, and Uechi methods -- using spot urinary sampling for 24-h urinary sodium (U-Na) prediction in hypertensive patients living in northeast China. Methods: There were 1154 hypertensive patients enrolled from multiple centers. Five different formulas were used to predict 24-h U-Na excretion via spot morning urinary samples. Actual U-Na excretion was measured from 24-h urine samples. The estimated value was compared with the actual value by examining biases, the intraclass correlation coefficients (ICC), and Bland-Altman plots. Results: The average excretion of sodium was 2.97 +/- 1.26 g/day. The formula-produced mean biases for actual U-Na were 0.31 g/day for INTERSALT, 0.80 g/day for Mage, 0.88 g/day for Tanaka, 1.14 g/day for Uechi, and 1.95 g/day for Kawasaki. The ICC was 0.511 for Kawasaki, 0.499 for INTERSALT, 0.468 for Tanaka, 0.402 for Mage, and 0.378 for Uechi. The least mean bias in the lower and moderate salt intake subgroups was 1.22 and 0.07 g/day, respectively, which was calculated using the Mage and INTERSALT methods. The least mean bias in the higher salt intake subgroup was 0.10 g/day for the Uechi method. The INTERSALT method was more efficiency at the individual level, with 17.4% of participants having relative differences within 10%, and 22.3% participants having absolute differences within 393 mg. Conclusion: The INTERSALT method may exhibit a good performance in estimating 24-h urinary sodium level for the hypertensive population living in northeast China.