Supplementary Material for: Feasibility of assessment of habitual salt intake using a 24-hour urinary salt excretion self-measuring device

Introduction: To assess habitual salt intake, tools are needed to measure 24-h urinary salt excretion repeatedly. We developed and validated a new portable salt monitor, which measures salt excreted per urination and sums the values to provide an accurate estimate of urinary salt excretion over 24 h. Methods: A previously developed salt monitor was improved with respect to the capacity, volume sensors, and equation for urinary sodium chloride concentration estimation. In 20 healthy Japanese female volunteers, 24-h urinary salt excretion was measured using the salt monitor and a conventional 24-h urine collection method on eight non-consecutive days. Results: In a total of 157 days, there were no fixed or proportional errors between the methods. The mean salt intake over 8 days was 8.5 ± 2.0 g/day for the 24-h urine collection and 8.3 ± 2.3 g/day for the salt monitor, showing a strong correlation (r = 0.912, p < 0.001). At a cut-off value of 6 g, the salt monitor was able to completely classify individuals by habitual salt intake. Discussion/Conclusion: The validity of the new salt monitor was confirmed. The device can be considered an alternative to the traditional 24-h urine collection for repeated surveys and for self-management of daily salt intake.