Effects of a Hypertension Management Mobile App on Urinary Sodium Excretion in Patients With Chronic Kidney Disease: Randomized Controlled Trial.

Background: Excessive salt intake is detrimental to the kidneys. Nevertheless, salt restriction is often suboptimal in patients with chronic kidney disease (CKD). Smartphone app-based interventions might help reduce salt intake by supporting self-monitoring and behavior change at scale. However, clinical trials evaluating these interventions for salt reduction are limited, particularly in CKD populations. Objective: This study investigated whether a hypertension management app could reduce urinary sodium excretion in patients with CKD. Methods: This open-label, single-center, randomized clinical trial included 101 patients with CKD who had a history of hypertension and estimated 24-hour urinary sodium excretion of 100 mmol or greater. Patients in the intervention group used CureApp HT, a smartphone app designed to manage hypertension through lifestyle modifications and self-monitoring, particularly for salt restriction. The app delivered daily, individualized guidance tailored to each patient's lifestyle. Patients also received lifestyle counseling by nephrologists during outpatient visits. The control group received lifestyle counseling alone. The intervention period was 12 weeks. The primary outcome was the change in estimated 24-hour urinary sodium excretion from baseline to week 12, calculated from spot urine samples using the Tanaka method. Key secondary outcomes included office blood pressure, brachial-ankle pulse wave velocity, urinary protein-to-creatinine ratio, and plasma brain natriuretic peptide. The analysis was conducted in the intention-to-treat population, using a mixed-effects model for repeated measures. Results: A total of 101 patients were randomly assigned to the intervention group (n=51) or the control group (n=50). The median (IQR) app engagement rate, calculated by dividing the number of days patients recorded blood pressure in the app by the total intervention period, was 96% (73%-99%). The mean (SD) baseline estimated glomerular filtration rate and 24-hour urinary sodium excretion were 38 (18) mL/min/1.73 m2 and 145 (33) mmol, respectively. A higher proportion of patients in the intervention group reported that their salt intake behaviors had "significantly improved" or "somewhat improved" by the intervention than those in the control group (35/46, 76% vs 18/47, 38%; P<.001). However, the mean change in estimated 24-hour urinary sodium excretion during the intervention period did not differ significantly between groups (1.4, 95% CI -12.0 to 14.7 mmol in the intervention group vs 2.5, 95% CI -10.7 to 15.6 mmol in the control group; between-group difference -1.1, 95% CI -19.8 to 17.7 mmol; P=.92). Secondary outcomes were not significantly different between groups. These outcomes were not altered even in a subgroup of patients reporting improved self-reported salt intake behaviors. Conclusions: The smartphone app did not reduce salt intake in patients with CKD, despite a substantial improvement in self-reported salt intake behaviors. Enhancing the intervention intensity may be necessary to effectively bridge the intention-behavior gap.