Spot urine samples compared to 24-hour urine samples for estimating changes in urinary sodium and potassium excretion in the China salt substitute and stroke study

Journal article

Background: The capacity of spot urine samples for detecting changes in dietary sodium and potassium intake is unclear. Methods: Changes in sodium and potassium intake, over a 6-month to 2-year interval, were measured from 24-hour urine samples and estimated from spot urine samples using several published methods in 3270 Chinese. Additional estimates were made by multiplying individual spot sodium and potassium concentrations by a single estimated 24-hour urine volume derived from external data. Results: The measured difference in 24-hour intake between intervention and control groups was -0.35g (95%CI: -0.68 to -0.02g; p=0.039) for sodium and 0.66g (95%CI: 0.52 to 0.80g; p<0.001) for potassium, based upon 24-hour urine samples. The corresponding estimates of sodium differences for the Tanaka (-0.06g), Kawasaki (-0.09g), Intersalt without potassium (-0.09g) and Intersalt with potassium (-0.14g) equations were all smaller and not clearly different (all p>0.10). The estimates were -0.65g for sodium and 1.11g for potassium using individual spot urine concentrations and an externally derived standard urine volume (both p <0.01). Conclusions: The published equations were unable to detect the differences in sodium intake measured by 24-hour urine samples in our study. A simpler method based upon spot urine electrolyte concentrations and a standard urine volume may offer an alternative approach to measuring differences in sodium and potassium intakes between population groups without requiring 24-hour urine, but will need further investigation.

Authors: Huang, L; Woodward, M; Stepien, S; Tian, M; Yin, X

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: International Journal of Epidemiology
• Volume: 47
• Issue: 6
• Pages: 1811–1820
• Publication date: 2018-10-10
• Acceptance date: 2018-08-26
• DOI: 10.1093/ije/dyy206
• EISSN: 1464-3685
• ISSN: 0300-5771
• Keywords: random allocation; 24-hour urine; potassium; sodium; spot urine; controlled trial