The Exploratory And Application Study Of Estimation Method Of 24-hour Urinary Sodium Excretion By Using Spot Urine For Chinese Population

Background Several studies have confirmed dietary salt intake is positively associated with hypertension. While several guidelines included recommendations regarding dietary sodium intake and take the salt reduction strategy as one of important lifestyle interventions.24-h urinary sodium excretion (24-h USE) is the preferred method and is considered the gold standard for assessing dietary salt intake, including Kawasaki formula (K), INTERSALT formula (I) and Tanaka formula (T), which all modeled from developed countries.Objectives To develop and validate of the new estimation methods for 24-h urinary sodium excretion by using spot urine for Chinese residents.Methods 100 healthy participants were enrolled in this study (Xishan population) and they all collected each spot urine sample and mixed finally as the 24-hour urine samples according to the study design and protocol. Data from previous researches were also used in this study, including Prospective Urban Rural Epidemiology study-China urine validation trial population (PURE-China urine trial population,425 participants) and Application of prevention and treatment technique in community for noncommunicable diseases (Dexing population,152 participants), for which these two researches were both only collected the morning urine and 24-hour urine samples. Eliminated the data, whose urinary creatinine concentration was exceeding the normal range for adults, the various model establishment paths was taken. (1) 77 training dataset from Xishan population was used to modeled New method Ⅰ. PURE-China urine trial population (n=331) and Dexing population (n=133) were applied as the external validation dataset to assess the accuracy of New method Ⅰ for estimation of 24-h USE in Chinese. (2) The merged population from three independent researches were randomized and re-sampled as training and validation dataset with 7:3 ratio (541 training samples to 162 validation samples). The model established by using linear model step by step. And the validation analysis conducted through correlation, bias distribution, residual analysis and Bland-Altman plot to assess the accuracy and the applicability of New methods (Ⅰ and Ⅱ) in Chinese residents.24-h USE was estimated by using New methods and Kawasaki formulae to evaluated the salt intake in PURE-China baseline population. Subgroup analysis was also performed to explore the salt intake gap in different population characteristics.Results Two New methods for 24-h USE estimation using spot urine were modeled and finally established.Random urine New method Ⅰ:Male:PrCRE24h=11.87×weight(kg)+0.417×height(cm)-11.47×age+832.566Female:PrCRE24h=9.638×weight(kg)-0.085×height(cm)-3.337×age+490.743 e-24-h USE=2.06xPrUCr24hx×(NaRU/CrRU)0.431Second morning urine New method Ⅱ:Male:PrCRE24h=9.39xweight(kg)-3.567xheight(cm)-4.683xage+1498.014 Female:PrCRE24h=8.09xweight(kg)+4.417×height(cm)-1.906xage-159.528 e-24-h USE=2.41×PrUCr24h×(NasMu/CrSMU)0.461New method Ⅰ, with big bias at population level, underestimated the mean value of 24-h USE about 1311 mg/day. The bias distribution both in relative and absolute bias showed a poorer accuracy of 24-h USE at individual level. Compared with K, I, T methods, the accuracy of estimation of K method was better than others. New method Ⅱ underestimated the mean value of 24-h USE about 273 mg/day, which was better for population level estimation. Furthermore, the accuracy of estimation at individual level also was not improved through bias distribution analysis. With the similar effect of K method, New method Ⅱ showed a dispersed randomly Bland-Altman plot and indicated a relative accuracy. Although the gap between estimation values and real measured values was the least by using New method Ⅱ (Estimated-Measured), the bias of individual estimated values were all big no matter which methods used.24-h USE means of Chinese urban and rural residents from PURE-China baseline population by using New method Ⅱ was 5142 mg/day, which amounted to 13.06 g/day after transform the salt equivalent. Residents live in North area, or Eastern region with the higher sodium excretion. The salt intake might higher in rural area than that in urban. The differences between higher education level and lower level was significant statistically. Furthermore, salt intake was higher in hypertension population, and the effects to blood pressure by salt or sodium were much more severe in normotension people than that in hypertension people.Conclusions The estimation for 24-h USE by using spot urine through New methods Ⅰ and Ⅱ did not showed a good accuracy at individual level. So this method might be not recommended to apply. However, New Ⅱ method, which was similar with Kawasaki formula, could be an alternative for 24-h USE estimation at population level to evaluate the salt intake in given population. The means of salt intake of Chinese residents estimated through spot urine methods indicated an incredible high level, about 2.6 times over the recommendation of salt daily intake by WHO.