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.

Smartphone Application-Assisted Home Blood Pressure Monitoring Compared With Office and Ambulatory Blood Pressure Monitoring in Patients With Hypertension: the AMUSE-BP Study.

BACKGROUND: The development of automated, smartphone application (app)-assisted home blood pressure monitoring (HBPM) allows for standardized measurement of blood pressure (BP) at home. The aim of this study was to evaluate the (diagnostic) agreement between app-assisted HBPM, automated office BP (OBP), and the reference standard 24-hour ambulatory BP monitoring (ABPM). METHODS: In this open randomized 5-way cross-over study, patients diagnosed with hypertension were randomized to one of 10 clusters, each containing 5 BP measurement methods (ABPM, HBPM, attended OBP, unattended OBP, and unattended 30-minute BP) in different order. RESULTS: In total, 113 patients were included. The average 24-hour ABPM was 126±11/73±8 mm Hg compared with 141±14/82±10 mm Hg with app-assisted HBPM, 134±13/80±9 mm Hg with unattended 30-minute BP, 137±16/81±11 mm Hg with attended OBP, and 135±15/81±10 mm Hg with unattended OBP monitoring. Diagnostic agreement between app-assisted HBPM and 24-hour ABPM for diagnosing sustained (OBP >140/90 mm Hg and ABPM ≥130/80 mm Hg or HBPM ≥135/85 mm Hg), white-coat (OBP ≥140/90 mm Hg and ABPM <130/80 mm Hg or HBPM <135/85 mm Hg), and masked hypertension (OBP <140/90 mm Hg and ABPM ≥130/80 mm Hg or HBPM ≥135/85 mm Hg) was fair-to-moderate (κ statistics ranging from 0.34 to 0.40). App-assisted HBPM had high sensitivities (78%-91%) and negative predictive values (90%-97%) for diagnosing sustained and masked hypertension. CONCLUSIONS: This study showed a considerable (diagnostic) disagreement between app-assisted HBPM and ABPM. App-assisted HBPM had high sensitivity in the diagnosis of sustained and masked hypertension and may therefore be used as complementary to, but not a replacement of, ABPM.