VERIFY AND EVALUATE FOUR SPOT URINARY METHODS FOR ESTIMATING 24-HOUR URINARY SODIUM EXCRETION RATE IN TIBETAN POPULATION

Abstract

Objective: To verify and evaluate four spot urinary methods for estimating 24-hour urinary sodium excretion rate in Tibetan population (Kawasaki method, Tanaka method, INTERSALT method and SH2 method). Design and method: 323 subjects were selected from the Ganzi Tibetan Autonomous Prefecture of Sichuan Province, China. The morning second urine samples and 24 hours urine samples were collected. The concentrations of creatinine, sodium and potassium in the morning second urine samples and 24 hours urine samples were measured. To compare the mean deviation, correlation, and consistency between the measured values and estimated 24-hour urinary sodium excretion by Kawasaki method, Tanaka method, INTERSALT method and SH2 method. Results: The average differences between the estimated values and measured values by Kawasaki method, Tanaka method, INTERSALT method and SH2 method were 124.86 mg/days, -937.58 mg/days, -1314.15 mg/days and -1747.436 mg/days, respectively. The correlation coefficient with the measured values was 0.434, 0.38, 0.273 and 0.348, respectively. The intraclass correlation coefficient was higher for Kawasaki method (0.473) than for Tanaka method (0.397), INTERSALT method (0.269) and SH2 method (0.348). The Bland Altman analysis showed 3.4%, 6.2%, 5.9% and 5.6% of the subjects’ estimated values exceeded the consistent boundary of ± 1.96 for Kawasaki method, Tanaka method, INTERSALT method and SH2 method. When four spot urinary sodium methods used for evaluating the individual salt intake, the misclassification rate was more than 45%. Compared with the other three methods, the misclassification probability of Kawasaki method was 48.2%, while the misclassification probability of Tanaka, INTERSALT and SH2 methods was 72.1%, 75.5% and 74.6%, respectively. However, when individual's salt intake was higher than 12.8 g/days, the probability of misclassification of Kawasaki method, Tanaka method, INTERSALT method and SH2 method was 20%, 90%, 97.5% and 97.5%, respectively. Conclusions: When the Kawasaki method is used to evaluate the salt intake of Tibetan population, the deviation, consistency and reproducibility were better than Tanaka method, INTERSALT method and SH2 method. It was especially suitable for the evaluation of 24-hour urinary sodium excretion rate of people with high salt intake. It can be used to investigate the salt intake of Tibetan population in a large-scale epidemiological study.