Development of objective indicators for quantitative analysis of sodium intake: the sodium to potassium ratio of second-void urine is correlated with 24-hour urinary sodium excretion

  • Kim, Jung Gon (Department of Internal Medicine, Inje University Ilsan-Paik Hospital) ;
  • Han, Sang-Woong (Department of Internal Medicine, Hanyang University Guri Hospital) ;
  • Yi, Joo Hark (Department of Internal Medicine, Hanyang University Guri Hospital) ;
  • Park, Hyeong Cheon (Department of Internal Medicine, Yonsei University Gangnam Hospital) ;
  • Han, Sang Youb (Department of Internal Medicine, Inje University Ilsan-Paik Hospital)
  • Received : 2019.04.17
  • Accepted : 2019.08.13
  • Published : 2020.02.01


BACKGROUND/OBJECTIVES: To date, sodium intake has been evaluated based on spot urine instead of 24-hour (hr) urine collection. Nevertheless, the optimal method for assessing daily sodium intake remains unclear. SUBJECTS/METHODS: Fifteen male (age 32.7 ± 6.5 years) participants were offered 3 meals with a total of 9-10 g salt over 24 hours, and 24-hr urine was collected from the second-void urine of the first day to the first-void urine of the second day. Twenty-four-hr urinary sodium (24UNa) was estimated using Tanaka's equation and the Korean formula, and spot urine Na, potassium (K), chloride (Cl), urea nitrogen (UN), creatinine (Cr), specific gravity (SG) and osmolality (Osm) were measured. The ratios of urinary Na to other parameters were calculated, and correlations with total measured 24UNa were identified. RESULTS: Average 24-hr urine volume was 1,403 ± 475 mL, and measured 24UNa was 143.9 ± 42.1 mEq (range, 87.1-239.4 mEq). Measured 24UNa was significantly correlated with urinary Na/UN (r = 0.560, P < 0.01), urinary Na/Osm (r = 0.510, P < 0.01), urinary Na/Cr (r = 0.392, P < 0.01), urinary Na/K (r = 0.290, P < 0.01), 24UNa estimated using Tanaka's equation (r = 0.452, P < 0.01) and the Korean formula (r = 0.414, P < 0.01), age (r = 0.548, P < 0.01), weight (r = 0.497, P < 0.01), and height (r = 0.393, P < 0.01) in all spot urine samples. Estimated 24UNa based on the second-void spot urine of the first day tended to be more closely correlated with measured 24UNa than were estimates from the other spot urine samples. The significant parameters correlated with the second-void urine of the first day were urinary Na/K (r = 0.647, P < 0.01), urinary Na/Cr (r = 0.558, P < 0.05), and estimated 24UNa using Tanaka's equation (r = 0.616, P < 0.05) and the Korean formula (r = 0.588, P < 0.05). CONCLUSIONS: Second-void urine is more reliable than first-void urine for estimating 24UNa. Urinary Na/K in the second-void urine on the first day is significantly correlated with 24UNa. Further studies are needed to establish the most reliable index and the optimal time of urine sampling for predicting 24UNa.


  1. Aburto NJ, Ziolkovska A, Hooper L, Elliott P, Cappuccio FP, Meerpohl JJ. Effect of lower sodium intake on health: systematic review and meta-analyses. BMJ 2013;346:f1326.
  2. Jones-Burton C, Mishra SI, Fink JC, Brown J, Gossa W, Bakris GL, Weir MR. An in-depth review of the evidence linking dietary salt intake and progression of chronic kidney disease. Am J Nephrol 2006;26:268-75.
  3. Swift PA, Markandu ND, Sagnella GA, He FJ, MacGregor GA. Modest salt reduction reduces blood pressure and urine protein excretion in black hypertensives: a randomized control trial. Hypertension 2005;46:308-12.
  4. Intersalt Cooperative Research Group. Intersalt: an international study of electrolyte excretion and blood pressure. Results for 24 hour urinary sodium and potassium excretion. BMJ 1988;297:319-28.
  5. Ha SK. Dietary salt intake and hypertension. Electrolyte Blood Press 2014;12:7-18.
  6. McLean RM. Measuring population sodium intake: a review of methods. Nutrients 2014;6:4651-62.
  7. Brown IJ, Dyer AR, Chan Q, Cogswell ME, Ueshima H, Stamler J, Elliott P; 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;177:1180-92.
  8. Cogswell ME, Loria CM, Terry AL, Zhao L, Wang CY, Chen TC, Wright JD, Pfeiffer CM, Merritt R, Moy CS, Appel LJ. Estimated 24-hour urinary sodium and potassium excretion in US adults. JAMA 2018;319:1209-20.
  9. Komiyama Y, Kurosaki M, Nakanishi H, Takahashi Y, Itakura J, Yasui Y, Tamaki N, Takada H, Higuchi M, Gotou T, Kubota Y, Takaura K, Hayashi T, Oh W, Okada M, Enomoto N, Izumi N. Prediction of diuretic response to tolvaptan by a simple, readily available spot urine Na/K ratio. PLoS One 2017;12:e0174649.
  10. El-Bokl MA, Senousy BE, El-Karmouty KZ, Mohammed IK, Mohammed SM, Shabana SS, Shalaby H. Spot urinary sodium for assessing dietary sodium restriction in cirrhotic ascites. World J Gastroenterol 2009;15:3631-5.
  11. Colin-Ramirez E, Arcand J, Ezekowitz JA. Estimates of dietary sodium consumption in patients with chronic heart failure. J Card Fail 2015;21:981-8.
  12. Mills KT, Chen J, Yang W, Appel LJ, Kusek JW, Alper A, Delafontaine P, Keane MG, Mohler E, Ojo A, Rahman M, Ricardo AC, Soliman EZ, Steigerwalt S, Townsend R, He J; Chronic Renal Insufficiency Cohort (CRIC) Study Investigators. Sodium excretion and the risk of cardiovascular disease in patients with chronic kidney disease. JAMA 2016;315:2200-10.
  13. Boudville N, Ward S, Benaroia M, House AA. Increased sodium intake correlates with greater use of antihypertensive agents by subjects with chronic kidney disease. Am J Hypertens 2005;18:1300-5.
  14. Livingstone MB, Prentice AM, Strain JJ, Coward WA, Black AE, Barker ME, McKenna PG, Whitehead RG. Accuracy of weighed dietary records in studies of diet and health. BMJ 1990;300:708-12.
  15. Johnson RK, Goran MI, Poehlman ET. Correlates of over- and underreporting of energy intake in healthy older men and women. Am J Clin Nutr 1994;59:1286-90.
  16. Tanaka T, Okamura T, Miura K, Kadowaki T, Ueshima H, Nakagawa H, Hashimoto T. 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.
  17. Koo HS, Kim YC, Ahn SY, Oh SW, Kim S, Chin HJ, Park JH. Estimating 24-hour urine sodium level with spot urine sodium and creatinine. J Korean Med Sci 2014;29 Suppl 2:S97-102.
  18. Mann SJ, Gerber LM. Estimation of 24-hour sodium excretion from spot urine samples. J Clin Hypertens (Greenwich) 2010;12:174-80.
  19. Iwahori T, Miura K, Ueshima H, Chan Q, Dyer AR, Elliott P, Stamler J; INTERSALT Research Group. Estimating 24-h urinary sodium/potassium ratio from casual ('spot') urinary sodium/potassium ratio: the INTERSALT Study. Int J Epidemiol 2017;46:1564-72.
  20. Tabara Y, Takahashi Y, Kumagai K, Setoh K, Kawaguchi T, Takahashi M, Muraoka Y, Tsujikawa A, Gotoh N, Terao C, Yamada R, Kosugi S, Sekine A, Yoshimura N, Nakayama T, Matsuda F; Nagahama study group. Descriptive epidemiology of spot urine sodium-to-potassium ratio clarified close relationship with blood pressure level: the Nagahama study. J Hypertens 2015;33:2407-13.
  21. Iwahori T, Ueshima H, Miyagawa N, Ohgami N, Yamashita H, Ohkubo T, Murakami Y, Shiga T, Miura K. Six random specimens of daytime casual urine on different days are sufficient to estimate daily sodium/potassium ratio in comparison to 7-day 24-h urine collections. Hypertens Res 2014;37:765-71.
  22. Iwahori T, Ueshima H, Torii S, Saito Y, Fujiyoshi A, Ohkubo T, Miura K. Four to seven random casual urine specimens are sufficient to estimate 24-h urinary sodium/potassium ratio in individuals with high blood pressure. J Hum Hypertens 2016;30:328-34.
  23. Stamler J, Rose G, Stamler R, Elliott P, Dyer A, Marmot M. INTERSALT study findings. Public health and medical care implications. Hypertension 1989;14:570-7.
  24. Huggins CE, O'Reilly S, Brinkman M, Hodge A, Giles GG, English DR, Nowson CA. Relationship of urinary sodium and sodium-topotassium ratio to blood pressure in older adults in Australia. Med J Aust 2011;195:128-32.
  25. Hedayati SS, Minhajuddin AT, Ijaz A, Moe OW, Elsayed EF, Reilly RF, Huang CL. Association of urinary sodium/potassium ratio with blood pressure: sex and racial differences. Clin J Am Soc Nephrol 2012;7:315-22.
  26. Perez V, Chang ET. Sodium-to-potassium ratio and blood pressure, hypertension, and related factors. Adv Nutr 2014;5:712-41.
  27. Cook NR, Obarzanek E, Cutler JA, Buring JE, Rexrode KM, Kumanyika SK, Appel LJ, Whelton PK; Trials of Hypertension Prevention Collaborative Research Group. Joint effects of sodium and potassium intake on subsequent cardiovascular disease: the Trials of Hypertension Prevention follow-up study. Arch Intern Med 2009;169:32-40.
  28. da Silva OM, Thiele GB, Fayad L, Lazzarotto C, Dantas-Correa EB, de Lucca Schiavon L, Narciso-Schiavon JL. Comparative study of spot urine Na/K ratio and 24-hour urine sodium in natriuresis evaluation of cirrhotic patients with ascites. GE J Port Gastrenterol 2014;21:15-20.
  29. Iwahori T, Miura K, Ueshima H. Time to consider use of the sodium-to-potassium ratio for practical sodium reduction and potassium increase. Nutrients 2017;9:700.
  30. Wang CY, Cogswell ME, Loria CM, Chen TC, Pfeiffer CM, Swanson CA, Caldwell KL, Perrine CG, Carriquiry AL, Liu K, Sempos CT, Gillespie CD, Burt VL. Urinary excretion of sodium, potassium, and chloride, but not iodine, varies by timing of collection in a 24-hour calibration study. J Nutr 2013;143:1276-82.
  31. Kamata K, Tochikubo O. Estimation of 24-h urinary sodium excretion using lean body mass and overnight urine collected by a pipe-sampling method. J Hypertens 2002;20:2191-7.
  32. Ministry of Health and Welfare, Korea Centers for Disease Control and Prevention. Korea Health Statistics 2016: Korea National Health and Nutrition Examination Survey (KNHANES VII-1). Cheongju: Korea Centers for Disease Control and Prevention; 2017.
  33. Dougher CE, Rifkin DE, Anderson CA, Smits G, Persky MS, Block GA, Ix JH. Spot urine sodium measurements do not accurately estimate dietary sodium intake in chronic kidney disease. Am J Clin Nutr 2016;104:298-305.
  34. Arcand J, Floras JS, Azevedo E, Mak S, Newton GE, Allard JP. Evaluation of 2 methods for sodium intake assessment in cardiac patients with and without heart failure: the confounding effect of loop diuretics. Am J Clin Nutr 2011;93:535-41.