Patient self-assessment of urine dipsticks to estimate sodium intake in patients with hypertension.

Background & Aims: Dietary sodium restriction is recommended by current guidelines to reduce blood pressure and decrease the risk of cardiovascular disease. Current methods to assess sodium intake such as dietary questionnaires and 24-h urine collection are cumbersome, and the results are not readily available to patients. In this analysis, we evaluated using chloride and creatinine dipsticks as a convenient method to monitor sodium intake, in addition to patients' ability to practice this method independently.

Methods: This is a post-hoc analysis of a previously published trial, LowSalt4Life, that measured change in sodium consumption over 8 weeks to evaluate the effect of a just-in-time adaptive mobile application intervention. Participants were instructed on how to complete and interpret Quantab® chloride and Multistix® PRO 10 LS creatinine dipstick measurements at home and upload a picture of their results. A pharmacy student interpreted the chloride dipsticks, and intraclass correlation coefficients (ICC) were calculated to assess interrater reliability between the participant and pharmacy student. Predicted 24-h sodium values were calculated by the Kawasaki and Mann methods and compared to actual 24-h sodium excretion.

Results: There was a strong interobserver correlation between interpretations of the chloride dipsticks, with the ICC values 0.90, 0.97, 0.99, and 0.98 at weeks 2, 4, 6, and 8, respectively. There was a moderate correlation between the dipstick predicted 24-h sodium excretion and actual 24-h sodium excretion at baseline (r = 0.506; P < 0.001), and a weak correlation at week 8 (r = 0.187; P = 0.217). When corrected creatinine values were used, the dipstick predicted 24-h sodium excretion correlated with the actual 24-h sodium excretion at baseline and week 8 (r = 0.512; P < 0.001 and r = 0.451; P = 0.002).

Conclusions: Our analysis suggests that chloride and creatinine dipsticks have the potential to predict total daily excretion of sodium. This method provides patients with an easy, convenient, and accurate method to assess sodium excretion at home. Further research is needed to identify the optimal timing of performing the dipstick analysis as well as ways to improve the creatinine measurement of the urine samples.

Trial Registration: ClinicalTrials.gov NCT03099343; https://clinicaltrials.gov/ct2/show/NCT03099343.