Visual Abstract

Introduction: The assessment of sodium intake is difficult due to low accuracy of dietary records and to the inconvenience of 24-h urine collections. Therefore, equations based on spot urine samples have been proposed to estimate sodium intake. In this study, we aimed to develop and to validate equations to estimate 24-h urinary sodium excretion (24hUNa) from several urine samples in chronic kidney disease (CKD) patients. Methods: Cross-sectional study with 76 CKD patients (males 55.3%; age: 64.5 [56.0–69.0] years; glomerular filtration rate 27.8 [24.7–32.1] mL/min). Sodium excretion was measured in 12-h daytime and 12-h nighttime collections; spot 1 (first urine of the day) and spot 2 (second urine of the day). By multivariable linear regression analysis, 4 equations were developed. The equations’ accuracy was evaluated by P30 test. Association between estimated and measured 24hUNa was assessed by intraclass correlation coefficient (ICC); mean differences and limits of agreement by Bland-Altman plot. Data from 51 CKD patients of other CKD outpatient clinic were used to validate the equation developed from spot 2. Results: The 4 equations showed significant (p < 0.001) ICC and relatively good accuracy when compared to 24hUNa (Daytime: ICC = 0.89; P30 = 84%; Nighttime: ICC = 0.90; P30 = 83%; spot 1: ICC = 0.85; P30 = 78%; and spot 2: ICC = 0.70; P30 = 76%). In validation set, the equation from spot 2 was moderately accurate (P30 = 67%). Mean bias and ICC were 19.9 mmol/day and 0.58 (p = 0.001), respectively. A high sensitivity (97%) and specificity (89%) were found for a cutoff of 3.6 g of sodium/day. Conclusion: Equations derived from 12 h collections better performed than spot urine when compared to gold standard 24hUNa. The equation from spot 2 showed good sensitivity to identify excessive sodium intake.

Bastos MG, Kirsztajn GM. Chronic kidney disease: importance of early diagnosis, immediate referral and structured interdisciplinary approach to improve outcomes in patients not yet on dialysis.
J Bras Nefrol
. 2011 Mar;33(1):93–108.
Williams ME, Garg R. Glycemic management in ESRD and earlier stages of CKD.
Am J Kidney Dis
. 2014 Feb;63(2 suppl 2):S22–38.
Lambers Heerspink HJ, de Borst MH, Bakker SJ, Navis GJ. Improving the efficacy of RAAS blockade in patients with chronic kidney disease.
Nat Rev Nephrol
. 2013 Feb;9(2):112–21.
Nerbass FB, Pecoits-Filho R, McIntyre NJ, McIntyre CW, Taal MW. High sodium intake is associated with important risk factors in a large cohort of chronic kidney disease patients.
Eur J Clin Nutr
. 2015 Jul;69(7):786–90.
He J, Mills KT, Appel LJ, Yang W, Chen J, Lee BT, et al.; Chronic Renal Insufficiency Cohort Study Investigators. Urinary Sodium and Potassium Excretion and CKD Progression.
J Am Soc Nephrol
. 2016 Apr;27(4):1202–12.
Bakris GL, Weir MR. Salt intake and reductions in arterial pressure and proteinuria. Is there a direct link?
Am J Hypertens
. 1996 Dec;9(12 Pt 2):200S–6S.
Kitiyakara C, Chabrashvili T, Chen Y, Blau J, Karber A, Aslam S, et al. Salt intake, oxidative stress, and renal expression of NADPH oxidase and superoxide dismutase.
J Am Soc Nephrol
. 2003 Nov;14(11):2775–82.
Thijssen S, Kitzler TM, Levin NW. Salt: its role in chronic kidney disease.
J Ren Nutr
. 2008 Jan;18(1):18–26.
Vegter S, Perna A, Postma MJ, Navis G, Remuzzi G, Ruggenenti P. Sodium intake, ACE inhibition, and progression to ESRD.
J Am Soc Nephrol
. 2012 Jan;23(1):165–73.
Lambers Heerspink HJ, Holtkamp FA, Parving HH, Navis GJ, Lewis JB, Ritz E, et al. Moderation of dietary sodium potentiates the renal and cardiovascular protective effects of angiotensin receptor blockers.
Kidney Int
. 2012 Aug;82(3):330–7.
Keyzer CA, van Breda GF, Vervloet MG, de Jong MA, Laverman GD, Hemmelder MH, et al.; Holland Nephrology Study (HONEST) Network. Effects of Vitamin D Receptor Activation and Dietary Sodium Restriction on Residual Albuminuria in CKD: The ViRTUE-CKD Trial.
J Am Soc Nephrol
. 2017 Apr;28(4):1296–305.
Bakris GL, Smith A. Effects of sodium intake on albumin excretion in patients with diabetic nephropathy treated with long-acting calcium antagonists.
Ann Intern Med
. 1996 Aug;125(3):201–4.
World Health Organization.
WHO Guideline: sodium intake for adults and children
. Geneva; 2012.
Kidney Disease Outcomes Quality Initiative (K/DOQI). K/DOQI clinical practice guidelines on hypertension and antihypertensive agents in chronic kidney disease.
Am J Kidney Dis
. 2004 May;43(5 suppl 1):S1–290.
McMahon EJ, Bauer JD, Hawley CM, Isbel NM, Stowasser M, Johnson DW, et al. A randomized trial of dietary sodium restriction in CKD.
J Am Soc Nephrol
. 2013 Dec;24(12):2096–103.
Campbell KL, Johnson DW, Bauer JD, Hawley CM, Isbel NM, Stowasser M, et al. A randomized trial of sodium-restriction on kidney function, fluid volume and adipokines in CKD patients.
BMC Nephrol
. 2014 Apr;15(1):57.
Nerbass FB, Pecoits-Filho R, McIntyre NJ, Shardlow A, McIntyre CW, Taal MW. Reduction in sodium intake is independently associated with improved blood pressure control in people with chronic kidney disease in primary care.
Br J Nutr
. 2015 Sep;114(6):936–42.
Saran R, Padilla RL, Gillespie BW, Heung M, Hummel SL, Derebail VK, et al. A randomized crossover trial of dietary sodium restriction in stage 3–4 CKD.
Clin J Am Soc Nephrol
. 2017 Mar;12(3):399–407.
Nerbass FB, Pecoits-Filho R, McIntyre NJ, McIntyre CW, Taal MW. Development of a formula for estimation of sodium intake from spot urine in people with chronic kidney disease.
Nephron Clin Pract
. 2014;128(1–2):61–6.
Dougher CE, Rifkin DE, Anderson CA, Smits G, Persky MS, Block GA, et al. Spot urine sodium measurements do not accurately estimate dietary sodium intake in chronic kidney disease.
Am J Clin Nutr
. 2016 Aug;104(2):298–305.
Kang SS, Kang EH, Kim SO, Lee MS, Hong CD, Kim SB. Use of mean spot urine sodium concentrations to estimate daily sodium intake in patients with chronic kidney disease.
. 2012 Mar;28(3):256–61.
Kutlugün AA, Arıcı M, Yıldırım T, Turgut D, Yılmaz R, Altındal M, et al. Daily sodium intake in chronic kidney disease patients during nephrology clinic follow-up: an observational study with 24-hour urine sodium measurement.
Nephron Clin Pract
. 2011;118(4):c361–6.
Hallvass AE, Claro LM, Gonçalves S, Olandoski M, Nerbass FB, Aita CA, et al. Evaluation of Salt Intake, Urinary Sodium Excretion and Their Relationship to Overhydration in Chronic Kidney Disease Patients.
Blood Purif
. 2015;40(1):59–65.
Elliott P, Brown I. Sodium intakes around the world. World Heal Organ Doc Prep Forum Tech Meet Reducing Salt Intake Popul Heal Organ, 2007.
McMahon EJ, Campbell KL, Mudge DW, Bauer JD. Achieving salt restriction in chronic kidney disease.
Int J Nephrol
. 2012;2012:720429.
Sarno F, Claro RM, Levy RB, Bandoni DH, Monteiro CA. [Estimated sodium intake for the Brazilian population, 2008-2009].
Rev Saude Publica
. 2013 Jun;47(3):571–8.
Kawasaki T, Itoh K, Uezono K, Sasaki H. A simple method for estimating 24 h urinary sodium and potassium excretion from second morning voiding urine specimen in adults.
Clin Exp Pharmacol Physiol
. 1993 Jan;20(1):7–14.
Tanaka T, Okamura T, Miura K, Kadowaki T, Ueshima H, Nakagawa H, et al. A simple method to estimate populational 24-h urinary sodium and potassium excretion using a casual urine specimen.
J Hum Hypertens
. 2002 Feb;16(2):97–103.
Brown IJ, Dyer AR, Chan Q, Cogswell ME, Ueshima H, Stamler J, et al.; INTERSALT Co-Operative Research Group. Estimating 24-hour urinary sodium excretion from casual urinary sodium concentrations in Western populations: the INTERSALT study.
Am J Epidemiol
. 2013 Jun;177(11):1180–92.
Nerbass FB, Hallvass AE, Taal MW, Pecoits-Filho R. Formula to detect high sodium excretion from spot urine in chronic kidney disease patients.
J Bras Nefrol
. 2017 Mar;39(1):23–8.
Whitton C, Gay GM, Lim RB, Tan LW, Lim WY, van Dam RM. Evaluation of Equations for Predicting 24-Hour Urinary Sodium Excretion from Casual Urine Samples in Asian Adults.
J Nutr
. 2016 Aug;146(8):1609–15.
Imai E, Yasuda Y, Horio M, Shibata K, Kato S, Mizutani Y, et al. Validation of the equations for estimating daily sodium excretion from spot urine in patients with chronic kidney disease.
Clin Exp Nephrol
. 2011 Dec;15(6):861–7.
Ogura M, Kimura A, Takane K, Nakao M, Hamaguchi A, Terawaki H. Estimation of salt intake from spot urine samples in patients with chronic kidney disease. 2012;13:36.
Black RM. Rose and Black’s Clinical Problems in Nephrology. 2o ed. Boston: Little, Brown and Company; 1996.
Churchill D, Taylor D, Keshaviah P; Canada-USA (CANUSA) Peritoneal Dialysis Study Group. Adequacy of dialysis and nutrition in continuous peritoneal dialysis: association with clinical outcomes.
J Am Soc Nephrol
. 1996 Feb;7(2):198–207.
Levey AS, Bosch JP, Lewis JB, Greene T, Rogers N, Roth D; Modification of Diet in Renal Disease Study Group. A more accurate method to estimate glomerular filtration rate from serum creatinine: a new prediction equation.
Ann Intern Med
. 1999 Mar;130(6):461–70.
Amano H, Kobayashi S, Terawaki H, Ogura M, Kawaguchi Y, Yokoo T. Measurement of daily sodium excretion in patients with chronic kidney disease; special reference to the difference between the amount measured from 24 h collected urine sample and the estimated amount from a spot urine.
Ren Fail
. 2018 Nov;40(1):238–42.
Kawasaki T, Ueno M, Uezono K, Kawano Y, Abe I, Kawazoe N, et al. The renin-angiotensin-aldosterone system and circadian rhythm of urine variables in normotensive and hypertensive subjects.
Jpn Circ J
. 1984 Feb;48(2):168–72.
Dyer AR, Martin GJ, Burton WN, Levin M, Stamler J. Blood pressure and diurnal variation in sodium, potassium, and water excretion.
J Hum Hypertens
. 1998 Jun;12(6):363–71.
Rhee MY, Kim JH, Shin SJ, Gu N, Nah DY, Park JH, et al. Estimating 24-Hour Urine Sodium From Multiple Spot Urine Samples.
J Clin Hypertens (Greenwich)
. 2017 Apr;19(4):431–8.
Koopman MG, Koomen GC, van Acker BA, Arisz L. Urinary sodium excretion in patients with nephrotic syndrome, and its circadian variation.
Q J Med
. 1994 Feb;87(2):109–17.
Fukuda M, Munemura M, Usami T, Nakao N, Takeuchi O, Kamiya Y, et al. Nocturnal blood pressure is elevated with natriuresis and proteinuria as renal function deteriorates in nephropathy.
Kidney Int
. 2004 Feb;65(2):621–5.
Agarwal R. Relationship between circadian blood pressure variation and circadian protein excretion in CKD.
Am J Physiol Renal Physiol
. 2007 Sep;293(3):F655–9.
Aoike DT, Baria F, Kamimura MA, Ammirati A, Cuppari L. Home-based versus center-based aerobic exercise on cardiopulmonary performance, physical function, quality of life and quality of sleep of overweight patients with chronic kidney disease.
Clin Exp Nephrol
. 2018 Feb;22(1):87–98.
Meuleman Y, Hoekstra T, Dekker FW, Navis G, Vogt L, van der Boog PJ, et al.; ESMO Study Group. Sodium Restriction in Patients With CKD: A Randomized Controlled Trial of Self-management Support.
Am J Kidney Dis
. 2017 May;69(5):576–86.
Lerchl K, Rakova N, Dahlmann A, Rauh M, Goller U, Basner M, et al. Agreement between 24-hour salt ingestion and sodium excretion in a controlled environment.
. 2015 Oct;66(4):850–7.
Copyright / Drug Dosage / Disclaimer
Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.
You do not currently have access to this content.