Validation and comparison of three formulae to estimate sodium and potassium excretion from a single morning fasting urine compared to 24-h measures in 11 countries

• Published in: Journal of hypertension Vol. 32; no. 5; p. 1005
• Main Authors: Mente, Andrew, O'Donnell, Martin J, Dagenais, Gilles, Wielgosz, Andy, Lear, Scott A, McQueen, Matt J, Jiang, Ying, Xingyu, Wang, Jian, Bo, Calik, K Burco T, Akalin, Ayse A, Mony, Prem, Devanath, Anitha, Yusufali, Afzal H, Lopez-Jaramillo, Patricio, Avezum, Jr, Alvaro, Yusoff, Khaled, Rosengren, Annika, Kruger, Lanthe, Orlandini, Andrés, Rangarajan, Sumathi, Teo, Koon, Yusuf, Salim
• Format: Journal Article
• Language: English
• Published: England 01.05.2014
• Subjects: Adult; Aged; Fasting; Female; Humans; Male; Middle Aged; Potassium - urine; Sodium - urine
• ISSN: 1473-5598
• DOI: 10.1097/HJH.0000000000000122

Although 24-h urinary measure to estimate sodium and potassium excretion is the gold standard, it is not practical for large studies. We compared estimates of 24-h sodium and potassium excretion from a single morning fasting urine (MFU) using three different formulae in healthy individuals. We studied 1083 individuals aged 35-70 years from the general population in 11 countries. A 24-h urine and MFU specimen were obtained from each individual. A subset of 448 individuals repeated the measures after 30-90 days. The Kawasaki, Tanaka, and INTERSALT formulae were used to estimate urinary excretion from a MFU specimen. The intraclass correlation coefficient (ICC) between estimated and measured sodium excretion was higher with Kawasaki (0.71; 95% confidence interval, CI: 0.65-0.76) compared with INTERSALT (0.49; 95% CI: 0.29-0.62) and Tanaka (0.54; 95% CI: 0.42-0.62) formulae (P <0.001). For potassium, the ICC was higher with the Kawasaki (0.55; 95% CI: 0.31-0.69) than the Tanaka (0.36; 95% CI: -0.07 to 0.60; P <0.05) formula (no INTERSALT formula exists for potassium). The degree of bias (vs. the 24-h urine) for sodium was smaller with Kawasaki (+313 mg/day; 95% CI: +182 to +444) compared with INTERSALT (-872 mg/day; 95% CI: -728 to -1016) and Tanaka (-548 mg/day; 95% CI: -408 to -688) formulae (P <0.001 and P = 0.02, respectively). Similarly for potassium, the Kawasaki formula provided the best agreement and least bias. Blood pressure correlated most closely and similarly with the 24-h and Kawasaki estimates for sodium compared with the other two formulae. In a diverse population, the Kawasaki formula is the most valid and least biased method of estimating 24-h sodium excretion from a single MFU and is suitable for population studies.