Kidney Res Clin Pract.  2018 Dec;37(4):373-383. 10.23876/j.krcp.17.0053.

Estimating the urinary sodium excretion in patients with chronic kidney disease is not useful in monitoring the effects of a low-salt diet

Affiliations
  • 1Department of Internal Medicine, Kyung Hee University Medical Center, Seoul, Korea. lshkidney@khu.ac.kr
  • 2Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam, Korea.
  • 3Department of Internal Medicine, Seoul National University Hospital, Seoul, Korea.
  • 4Department of Internal Medicine, Konkuk University School of Medicine, Seoul, Korea.
  • 5Department of Internal Medicine, Dongguk University Ilsan Hospital, Goyang, Korea.
  • 6Department of Internal Medicine, The Catholic University of Korea, Seoul St. Mary's Hospital, Seoul, Korea.
  • 7Department of Internal Medicine, SMG-SNU Boramae Medical Center, Seoul, Korea.
  • 8Department of Clinical Pharmacology, School of Medicine, Kyung Hee University, Seoul, Korea.

Abstract

BACKGROUND
Several epidemiologic studies have suggested that the urine sodium excretion (USE) can be estimated in lieu of performing 24-hour urine collection. However, this method has not been verified in patients with chronic kidney disease (CKD) or in an interventional study. The purpose of this study was to evaluate the usefulness of estimating USE in a prospective low-salt diet education cohort (ESPECIAL).
METHODS
A new formula was developed on the basis of morning fasting urine samples from 228 CKD patients in the ESPECIAL cohort. This formula was compared to the previous four formulas in the prediction of 24-hour USE after treatment with olmesartan and low-salt diet education.
RESULTS
Most previously reported formulas had low predictability of the measured USE based on the ESPECIAL cohort. Only the Tanaka formula showed a small but significant bias (9.8 mEq/day, P < 0.05) with a low correlation (r = 0.34). In contrast, a new formula showed improved bias (−0.1 mEq/day) and correlation (r = 0.569) at baseline. This formula demonstrated no significant bias (−1.2 mEq/day) with the same correlation (r = 0.571) after 8 weeks of treatment with olmesartan. Intensive low-salt diet education elicited a significant decrease in the measured USE. However, none of the formulas predicted this change in the measured urine sodium after diet adjustment.
CONCLUSION
We developed a more reliable formula for estimating the USE in CKD patients. Although estimating USE is applicable in an interventional study, it may be unsuitable for estimating the change of individual sodium intake in a low-salt intervention study.

Keyword

Chronic kidney disease; Low-salt diet; Sodium excretion

MeSH Terms

Bias (Epidemiology)
Cohort Studies
Diet
Diet, Sodium-Restricted*
Education
Epidemiologic Studies
Fasting
Humans
Methods
Prospective Studies
Renal Insufficiency, Chronic*
Sodium*
Urine Specimen Collection
Sodium
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