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
• Main Author: Mente A.; O'Donnell M.J.; Dagenais G.; Wielgosz A.; Lear S.A.; McQueen M.J.; Jiang Y.; Xingyu W.; Jian B.; Calik K.B.T.; Akalin A.A.; Mony P.; Devanath A.; Yusufali A.H.; Lopez-Jaramillo P.; Avezum A.; Yusoff K.; Rosengren A.; Kruger L.; Orlandini A.; Rangarajan S.; Teo K.; Yusuf S.
• Format: Article
• Language: English
• Published: Lippincott Williams and Wilkins 2014
• Online Access: https://www.scopus.com/inward/record.uri?eid=2-s2.0-84898488353&doi=10.1097%2fHJH.0000000000000122&partnerID=40&md5=95edecb8abd7fc2f3c07a53d7ff30df9

BACKGROUND AND OBJECTIVES: 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. METHODS: 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. RESULTS: 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 (+313mg/day; 95% CI: +182 to +444) compared with INTERSALT (-872mg/day; 95% CI: -728 to -1016) and Tanaka (-548mg/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. CONCLUSION: 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. © 2014 Wolters Kluwer Health / Lippincott Williams & Wilkins.