Variability of urinary salt excretion estimated by spot urine in treated hypertensive patients

Abstract

Among the several methods used to assess salt intake, estimating 24 h urinary salt excretion by spot urine seems appropriate for clinical practice. In this study, we investigated variability in urinary salt excretion using spot urine in hypertensive outpatients. Participants included 200 hypertensive patients who underwent spot urinary salt excretion at least three times during the observation period. Mean urinary salt excretion and the coefficient of the variation were 8.62 ± 1.96 g/day and 19.0 ± 10.2%, respectively. In the analysis of participants who underwent assessment of urinary salt excretion at least eight times (n = 54), a significant reduction in mean urinary salt excretion was found at the 5th measurement. On the contrary, the coefficient of the variation of urinary salt excretion continued to increase until the 5th measurement, and became stable thereafter. Mean urinary salt excretion was positively correlated with mean clinic diastolic blood pressure (r = 0.27, p < 0.05). Clinic diastolic blood pressure in the high urinary salt excretion group (≥10 g/day) was significantly higher than that of the low group (76.2 ± 7.5 vs 73.4 ± 8.3 mmHg, p < 0.05). Mean urinary salt excretion in summer was significantly lower than that of the other seasons (7.75 ± 1.94 vs 9.09 ± 2.68 (spring), 8.72 ± 2.12 (autumn), 8.92 ± 2.17 (winter) g/day, p < 0.01). In conclusion, repeated measurements of urinary salt excretion using spot urine are required to assess daily salt intake of hypertensive patients.