Abstract
Spot urine (SU) collection is a convenient method commonly used for sodium estimation, but its validity in predicting 24-h urinary sodium (24-hUNa) excretion has not been thoroughly evaluated among the general population. The aim of this study was to comprehensively assess the validity of eight existing methods in predicting 24-hUNa excretion by using SU samples among Chinese adults. We analyzed 1424 representative individuals aged 18 to 69 years. We compared the measured and estimated measurements of 24-hUNa at the population level by examining bias, the correlation, intraclass correlation coefficients (ICCs), receiver operating characteristic (ROC) curves and Bland–Altman plots and analyzed the relative and absolute differences and misclassification at the individual level. The bias for all methods was significant (all p < 0.001), among which the smallest bias was − 7.9 mmol for the Toft formula and the largest bias was − 53.8 mmol for the Mage formula. Correlation coefficients were all less than 0.380, all formulas exhibited an area under the ROC curve below 0.683, and the Bland–Altman plots indicated slightly high dispersion of the estimation biases at higher sodium levels regardless of the formula. The proportions of relative differences > 40% for the eight methods were all over one-third, the proportions of absolute differences > 51.3 mmol/24 h (3 g/day NaCl) were all over 40%, and the misclassification rates (7, 10, and 13 g/day NaCl as cutoff points) were all over 65%. Caution remains due to poor validity between estimated and actual measurements when using the eight formulas to obtain a plausible estimation for surveillance of the Chinese population sodium excretion, and the results do not support the application of SU to estimate sodium intake at the individual level due to its poor performance with respect to classification.
Highlights
Increased blood pressure (BP) has become a major risk factor for the global burden of disease
There is a certain difference between the estimated value of the prediction formula and the actual measurement value at the individual level, and the large differences in the characteristics of the population among different regions result in the limitation of the extrapolation of the prediction formula
The results of a systematic review and metaanalysis on 24-h urinary sodium excretion in China show that the sodium intake in southern China is relatively low (9.9 g/day), which is close to our research r esult[33]
Summary
Increased blood pressure (BP) has become a major risk factor for the global burden of disease. Reducing sodium intake in the general population, which has been considered a cost-effective action and recommended as one of the top three priority actions to tackle the global crisis of noncommunicable disease by the WHO, should be maintained and expanded to save more lives, prevent diseases and avoid c osts[7,8,9,10] Both to achieve goals such as a 30% relative reduction in mean population salt intake by 2025 set by WHO11 or 20% by 2030 set by the Chinese Central Government and given that the determination of salt intake is considered decisive in the individualization of therapy in patients with, for example, renal hypertension and resistant h ypertension[12], the highest priority and most essential step is to ensure that the mean population or individual salt intake can be correctly assessed and continuously monitored. We tested all hypotheses before formula verification and explored the conditions for the promotion and use of the prediction formula as while tried to find reasons for the bias
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