24-Hour vs. Spot Urinary Sodium and Potassium Measurements in Adult Hypertensive Patients: A Cohort Validation Study

Abstract

BACKGROUND Sodium intake is correlated with the development of hypertension. Guyton’s principals suggest that the 24-hour urinary sodium excretion reflects sodium ingestion over the same period. 24-hour urine collections are arduous to collect, so many centers use spot urinary measurements instead. We compared spot to matched 24-hour urinary electrolyte measurements. METHODS We examined 419 hypertensive patients from the UCL Complex Hypertension Clinic. 77 had matched and complete 24-hour and spot urinary and serum biochemistry to examine. We compared the spot and 24-hour urinary; sodium concentration, Na/Cr ratio, FENa, Kawasaki and Tanaka estimated sodium excretion as well as the potassium concentration, K/Cr ratio, Kawasaki and Tanaka potassium excretion. RESULTS Our cohort was 58% male and the median age was 41 years. The 24-hour and spot Na concentrations correlated moderately (r = 0.4633, P < 0.0001). The 24-hour and spot Na/creatinine ratios correlated weakly (r = 0.2625, P = 0.0194). The 24-hour and spot FENa results showed a weak negative correlation (r = −0.222, P = ns). The 24-hour sodium excretion and the Kawasaki-derived spot urine sodium excretion correlated moderately (r = 0.3118, P = 0.0052). All Bland–Altman analyses showed poor agreement. The 24-hour and spot potassium concentrations correlated very poorly (r = 0.1158, P = ns). The 24-hour and spot urinary K/creatinine ratios correlated weakly (r = 0.47, P ≤ 0.0001). 24-hour and Kawasaki and Tanaka estimated potassium excretions correlated much better (r = 0.58, P < 0.0001). CONCLUSIONS Spot urinary measurements of sodium give a very poor understanding of the natriuresis occurring over the same 24-hour period. The Kawasaki and Tanaka estimations of the 24-hour sodium excretion showed a much lower correlation than previously reported.

Relationship between basal sodium intake and the effects of dapagliflozin in albuminuric diabetic kidney disease

“…The most critical limitation, sodium intake, as estimated using urinary sodium excretion on the basis of single-spot urine sampling, may have contributed to large variations in the data. Some studies reported that urinary sodium-to-creatinine ratios derived from spot urine sampling correlated weakly with those derived from 24-h urine collection 55 . Multiple reports suggest sodium intake calculated using the Tanaka formula is biased with overestimation at lower levels and underestimation at higher levels [55][56][57][58][59] .…”

“…Some studies reported that urinary sodium-to-creatinine ratios derived from spot urine sampling correlated weakly with those derived from 24-h urine collection 55 . Multiple reports suggest sodium intake calculated using the Tanaka formula is biased with overestimation at lower levels and underestimation at higher levels [55][56][57][58][59] . A method such as 24-h urine collection may have provided a more accurate evaluation of sodium intake.…”

Effects of the 52% low-sodium salt applied to CM-DASH diet in hypertensive patients with type 2 diabetes：A Randomized Controlled Trial

“…The baseline mean salt consumption of participants in this study was 8.94g per day, but with the CM-DASH diet, the mean salt intake of participants was reduced by approximately 4g per day. As the golden criteria to determine the intake of sodium, 24-hour urine electrolyte electrolytes has been widely used in scientific research [18] .Our results shows that after the intervention of CM-DASH diet, the 24-hour urine Na + of the intervention group and the control group both decreased significantly, which indicated that CM-DASH diet had a marked effect on reducing the sodium intake of the participants. Studies have shown that high dietary sodium intake can lead to high BP by inhibiting the activity of Na + -K + -ATPase pumps in cell membrane [19] , damaging vascular endothelial function [20] and activating RAAS (Renin-Angiotension-Aldosterone System) [21] .…”

Serum aldosterone and urine electrolytes dynamics in response to DASH diet intervention – An inpatient mechanistic study

“…In a cross-sectional study, spot urine sodium ratio was compared to 24-hour collection content. 24-hour and spot sodium concentrations correlated moderately (r = 0.46) and gave a very poor understanding of the natriuresis occurring over the same 24-hour period, without relating to nutrition or potassium [45]. Correlation between Na þ /K þ ratios measured in spot urine vs. 24-hour collection was found to be statistically significant in another trial, yet the authors did not address intake or response to change in diet [46].…”