Estimating sodium intake from spot urine samples at population level: a validation and application study in French adults.

Abstract

The aim of this study was to assess the validity of the predictive INTERSALT equation using spot urine samples to estimate 24-hour urinary sodium (24-hUNa) excretion and daily sodium intake among the French adult population. Among 193 French adults ( validation sample ), we assessed the validity by comparing predicted 24-hUNa excretion from spot urine and measured 24-hUNa excretion from 24-hour urine collections. Spearman correlation coefficients and Bland-Altman plots were used and we calculated calibration coefficients. In a nationally representative sample of 1,720 French adults ( application sample ), the calibrated predictive equation was then applied to the spot urine Na values to estimate 24-hUNa excretion and daily Na intake. In that sample, predicted Na intake was compared to that estimated from 24-hour dietary recalls. Results were adjusted and corrected using calibration coefficients. In the validation sample, the measured 24-hUNa excretion was on average 14% higher than the predicted 24-hUNa (+ 13% for men and + 16% for women). Correlation between measured and predicted 24-hUNa excretion was moderate (Spearman r = 0.42) and the Bland-Altman plots showed underestimation at lower excretion level and overestimation at higher level. In the application study, estimated daily salt intake was 8.0\xa0g/day using dietary recalls, 8.1\xa0g/day using predicted INTERSALT equation and 9.3\xa0g/day after applying calibration coefficients calculated in the validation study. Despite overall underestimation of 24-hUNa excretion by spot urinary sodium, the use of predictive INTERSALT equation remains an acceptable alternative in monitoring global Na intake/excreted in the French population but its use is not advised at the individual level.