Spot Urine Samples to Estimate Na and K Intake in Patients With Chronic Kidney Disease and Healthy Adults: A Secondary Analysis From a Controlled Feeding Study

Published:December 09, 2020DOI:


      The objective of this study was to assess the agreement between estimated 24-hour urinary sodium excretion (e24hUNa) and estimated 24-hour urinary potassium excretion (e24hUK), calculated from a spot urine sample using several available equations and actual sodium and potassium intake from a controlled diet in both healthy participants and those with chronic kidney disease (CKD).

      Design and Methods

      This study is a secondary analysis of a controlled feeding study in CKD patients matched to healthy controls. Participants (n = 16) consumed the controlled diet, which provided ∼2400 mg Na/day and ∼3000 mg K/day, for 8 days. On days 7 and 8, participants consumed all meals and collected all urine in an inpatient research setting, and they were discharged on day 9. The day 7 morning spot urine sample was used to calculate e24hUNa and e24hUK, which was compared with known sodium and potassium intake, respectively.


      Average e24hUNa from the INTERSALT and Tanaka-Na equations were higher than actual sodium intake by 373 mg and 559 mg, respectively, though the differences were not significant. e24hUNa from the Nerbass-SALTED equation in CKD participants was significantly higher than actual sodium intake by ∼2000 mg (P < .001), though e24hUNa from the Nerbass-RRID equation was not different from intake. e24hUK from the Tanaka-K equation was significantly lower than actual potassium intake (P < .001). For both e24hUNa and e24hUK for all participants, agreement with actual intake was poor, and e24hUNa and e24hUK were not correlated with actual sodium or potassium intake, respectively.


      e24hUNa and e24hUK are poor indicators of true sodium and potassium intake, respectively, in both healthy and CKD participants. Findings should be confirmed in larger sample sizes with varying levels of dietary sodium and potassium.
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        • Benjamin E.J.
        • Muntner P.
        • Alonso A.
        • et al.
        Heart disease and Stroke Statistics-2019 Update: a report from the American Heart association.
        Circulation. 2019; 139: e56-e66
        • Mennuni S.
        • Rubattu S.
        • Pierelli G.
        • Tocci G.
        • Fofi C.
        • Volpe M.
        Hypertension and kidneys: unraveling complex molecular mechanisms underlying hypertensive renal damage.
        J Hum Hypertens. 2014; 28: 74-79
        • Sacks F.M.
        • Svetkey L.P.
        • Vollmer W.M.
        • et al.
        Effects on blood pressure of reduced dietary sodium and the dietary Approaches to Stop hypertension (DASH) diet. DASH-sodium Collaborative research group.
        N Engl J Med. 2001; 344: 3-10
        • He F.J.
        • MacGregor G.A.
        Effect of modest salt reduction on blood pressure: a meta-analysis of randomized trials. Implications for public health.
        J Hum Hypertens. 2002; 16: 761-770
        • McMahon E.J.
        • Bauer J.D.
        • Hawley C.M.
        • et al.
        A randomized trial of dietary sodium restriction in CKD.
        J Am Soc Nephrol. 2013; 24: 2096-2103
        • Garofalo C.
        • Borrelli S.
        • Provenzano M.
        • et al.
        Dietary salt restriction in chronic kidney disease: a meta-analysis of randomized clinical trials.
        Nutrients. 2018; 10
        • Filippini T.
        • Violi F.
        • D'Amico R.
        • Vinceti M.
        The effect of potassium supplementation on blood pressure in hypertensive subjects: a systematic review and meta-analysis.
        Int J Cardiol. 2017; 230: 127-135
        • Kieneker L.M.
        • Bakker S.J.
        • de Boer R.A.
        • Navis G.J.
        • Gansevoort R.T.
        • Joosten M.M.
        Low potassium excretion but not high sodium excretion is associated with increased risk of developing chronic kidney disease.
        Kidney Int. 2016; 90: 888-896
        • Sharma S.
        • McFann K.
        • Chonchol M.
        • de Boer I.H.
        • Kendrick J.
        Association between dietary sodium and potassium intake with chronic kidney disease in US adults: a cross-sectional study.
        Am J Nephrol. 2013; 37: 526-533
        • Einhorn L.M.
        • Zhan M.
        • Hsu V.D.
        • et al.
        The Frequency of hyperkalemia and its significance in chronic kidney disease.
        Arch Intern Med. 2009; 169: 1156-1162
        • An J.N.
        • Lee J.P.
        • Jeon H.J.
        • et al.
        Severe hyperkalemia requiring hospitalization: predictors of mortality.
        Crit Care. 2012; 16: R225
        • Holbrook J.T.
        • Patterson K.Y.
        • Bodner J.E.
        • et al.
        Sodium and potassium intake and balance in adults consuming self-selected diets.
        Am J Clin Nutr. 1984; 40: 786-793
        • Tasevska N.
        • Runswick S.A.
        • Bingham S.A.
        Urinary potassium is as reliable as urinary nitrogen for use as a recovery biomarker in dietary studies of free living individuals.
        J Nutr. 2006; 136: 1334-1340
        • Cogswell M.E.
        • Maalouf J.
        • Elliott P.
        • Loria C.M.
        • Patel S.
        • Bowman B.A.
        Use of urine Biomarkers to assess sodium intake: challenges and Opportunities.
        Annu Rev Nutr. 2015; 35: 349-387
        • McLean R.M.
        Measuring population sodium intake: a review of methods.
        Nutrients. 2014; 6: 4651-4662
        • Brown I.J.
        • Dyer A.R.
        • Chan Q.
        • et al.
        Estimating 24-hour urinary sodium excretion from casual urinary sodium concentrations in Western populations: the INTERSALT study.
        Am J Epidemiol. 2013; 177: 1180-1192
        • Tanaka T.
        • Okamura T.
        • Miura K.
        • et al.
        A simple method to estimate populational 24-h urinary sodium and potassium excretion using a casual urine specimen.
        J Hum Hypertens. 2002; 16: 97-103
        • 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; 20: 7-14
        • Nerbass F.B.
        • Pecoits-Filho R.
        • McIntyre N.J.
        • McIntyre C.W.
        • Taal M.W.
        Development of a formula for estimation of sodium intake from spot urine in people with chronic kidney disease.
        Nephron Clin Pract. 2014; 128: 61-66
        • Nerbass F.B.
        • Hallvass A.E.
        • Taal M.W.
        • Pecoits-Filho R.
        Formula to detect high sodium excretion from spot urine in chronic kidney disease patients.
        J Bras Nefrol. 2017; 39: 23-28
        • Hu J.
        • Wang Y.
        • Song N.
        • et al.
        Estimating 24-hour urinary sodium excretion from spot urine samples in chronic kidney disease patients.
        J Ren Nutr. 2020; 30: 11-21
      1. Intersalt: an international study of electrolyte excretion and blood pressure. Results for 24 hour urinary sodium and potassium excretion. Intersalt Cooperative Research Group.
        Bmj. 1988; 297: 319-328
        • Cogswell M.E.
        • Wang C.Y.
        • Chen T.C.
        • et al.
        Validity of predictive equations for 24-h urinary sodium excretion in adults aged 18-39 y.
        Am J Clin Nutr. 2013; 98: 1502-1513
        • Allen N.B.
        • Zhao L.
        • Loria C.M.
        • et al.
        The validity of predictive equations to estimate 24-hour sodium excretion: the MESA and CARDIA urinary sodium study.
        Am J Epidemiol. 2017; 186: 149-159
        • Charlton K.
        • Ware L.J.
        • Chidumwa G.
        • et al.
        Prediction of 24-hour sodium excretion from spot urine samples in South African adults: a comparison of four equations.
        J Hum Hypertens. 2019; 34: 24-33
        • Dougher C.E.
        • Rifkin D.E.
        • Anderson C.A.
        • et al.
        Spot urine sodium measurements do not accurately estimate dietary sodium intake in chronic kidney disease.
        Am J Clin Nutr. 2016; 104: 298-305
        • Mercado C.I.
        • Cogswell M.E.
        • Loria C.M.
        • et al.
        Validity of predictive equations for 24-h urinary potassium excretion based on timing of spot urine collection among adults: the MESA and CARDIA Urinary Sodium Study and NHANES Urinary Sodium Calibration Study.
        Am J Clin Nutr. 2018; 108: 532-547
        • He F.J.
        • Campbell N.R.C.
        • Ma Y.
        • MacGregor G.A.
        • Cogswell M.E.
        • Cook N.R.
        Errors in estimating usual sodium intake by the Kawasaki formula alter its relationship with mortality: implications for public health.
        Int J Epidemiol. 2018; 47: 1784-1795
        • He F.J.
        • Ma Y.
        • Campbell N.R.C.
        • MacGregor G.A.
        • Cogswell M.E.
        • Cook N.R.
        Formulas to estimate dietary sodium intake from spot urine alter sodium-mortality relationship.
        Hypertension. 2019; 74: 572-580
        • Campbell N.R.C.
        • He F.J.
        • Tan M.
        • et al.
        The International Consortium for Quality Research on Dietary Sodium/Salt (TRUE) position statement on the use of 24-hour, spot, and short duration (<24 hours) timed urine collections to assess dietary sodium intake.
        J Clin Hypertens (Greenwich). 2019; 21: 700-709