At-home determination of 24-h urine sodium excretion: Validation of chloride test strips and multiple spot samples.

Abstract

Sodium intake and compliance with dietary sodium modification are typically assessed using a 24-h urine collection analyzed using flame photometry, but this is inconvenient. Spot urine samples have been investigated as alternatives to 24-h collections, but their accuracy is poor. Since sodium and chloride are present in equal concentrations in dietary salt, chloride test strips may provide a suitable proxy for at-home measurement of urine sodium concentrations. We aimed to determine whether (i) chloride test strips provide a reliable measure of urinary sodium compared to the gold standard flame photometry and (ii) multiple spot samples accurately reflect 24-h urine sodium. We recruited 43 participants (19 males) aged 23.6±0.6years to complete multiple consecutive spot samples (morning and evening) along with a 24-h urine sodium collection. Urine 24-h sodium estimates using chloride test strips (114.6±7.5mmol/day) were highly correlated (r=0.900, p<0.0001) with flame photometry (121.1±7.7mmol/day) with a bias of -6.53±22.2mmol/day. Use of a three-spot sample average (both morning and evening spot samples) with a correction factor applied (122.9±4.1mmol/day) provided a good approximation of 24-h sodium measured by flame photometry (125.6±9.0mmol/day), with a bias of -2.55±43.9mmol/day. Chloride test strips applied to a 24-h urine collection provide a highly accurate measure of urinary sodium excretion, permitting convenient at-home sample collection and analysis. Their application to multiple spot samples provides a reasonable approximation of sodium excretion that can be used to conveniently monitor attempts at dietary sodium manipulation, without the inconvenience of completing a 24-h urine sample.