Validation of spot urine in estimating 24-h urinary sodium, potassium and sodium-to-potassium ratio during three different sodium diets in healthy adults

PURPOSE

To evaluate the validity of spot urine assay methods in estimating the 24-h urinary sodium, potassium and sodium-to-potassium ratio during three different sodium diets.

MATERIALS AND METHODS

Twelve healthy volunteers were asked to adhere to 3 dietary sodium targets (3.3-5.0g/day,<3.3 g/day and >5.0 g/day) for three consecutive weeks and to measure salt excretion daily in spot urine samples using a self-monitoring device. On day 7 of each week, 24-h urine was collected to compare measured with estimated 24-h salt excretion (by the Kawasaki, Tanaka and INTERSALT equations).

RESULTS

Correlation coefficients relating measured and estimated 24-h sodium excretion were low and not significant for Kawasaki and INTERSALT and moderate for the Tanaka equation (τ 0.56-0.64,p<.05). Bland-Altman plots showed considerable differences between estimated and measured sodium excretion across all salt diets. Over 40% of the participants showed an absolute difference between measured and estimated 24-h sodium of more than 1000 mg/day. The correlation coefficients between 24-h and spot Na/K ratio were 0.67, 0.94 and 0.85(p<.05), and mean differences were 0.59, 0.06 and 0.48 for the intermediate, low and high sodium diets, respectively.

CONCLUSION

These findings do not support estimation of individual 24-h salt excretion from spot urine by the Kawasaki, Tanaka, or INTERSALT formula. Plain language summaryAccurate monitoring of salt intake is essential to improve BP control. At present, measurement of sodium and potassium excretion in multiple non-consecutive 24-h urinary collections is considered the gold standard for measuring dietary sodium intake. However, this method is burdensome, time-consuming and error prone.Therefore, we assessed and compared the validity of three formula-based approaches to estimate 24-h urinary sodium and potassium excretion and the Na/K ratio from spot urine samples measured by a self-monitoring device under three different sodium diets using 24-h urine collections as the reference.We conclude that use of three commonly used equations that estimate 24-h urinary sodium and potassium excretion result in substantial bias, poor precision and poor accuracy and are therefore not recommended. The Na/K ratio based on multiple casual urine samples may be a useful, low-burden, low-cost alternative method to 24-h urine collection for monitoring daily salt intake.

A self-monitoring urinary salt excretion level measurement device for educating young women about salt reduction: A parallel randomized trial involving two groups

To prevent and treat hypertension, it is important to restrict salt in one's diet since adolescence. However, an effective salt-reduction education system has yet to be established. Besides accurate evaluation, we believe that the frequent usage of a measurement device may motivate individuals to avoid high salt intake. The present study evaluated the use of a urinary salt excretion measurement device for salt-reduction education in a parallel randomized trial of two groups. The sample comprised 100 university students who provided consent to participate. A survey with 24-hour home urine collection and blood pressure measurement was conducted. Participants in the self-monitoring group measured their own urinary salt excretion level for 4 weeks, using the self-measurement device. Analyses were conducted on 51 participants in the control group and 49 in the self-monitoring group. At baseline, there was no significant difference between the two groups in terms of their characteristics and 24-hour urinary salt excretion levels. After intervention, 24-hour urinary sodium/potassium ratio showed no change in the control group [baseline score: 4.1 ± 1.5; endline score: 4.2 ± 2.0; P = 0.723], but it decreased significantly in the self-monitoring group [baseline score: 4.0 ± 1.7; endline score: 3.5 ± 1.4; P = 0.044]. This change was significant even after adjusting for baseline and endline differences between groups using analysis of covariance (P = 0.045). The self-monitoring urinary salt excretion measurement device improved the 24-hour urinary sodium/potassium ratio. The device is a useful and practical tool for educating young individuals about dietary salt reduction.