To evaluate the capacity of spot urine samples to estimate mean population salt intake in Fiji and Samoa.Methods:
Mean salt intake was estimated from spot urine samples using six spot equations–Kawasaki, Tanaka, Mage, INTERSALT and Toft–and compared with the measured salt intake from 24-hour urine samples (24HUNa). Paired samples t-test was used to assess the difference between the two methods. Agreement was assessed through correlational analysis and Bland-Altman plots.Results:
A total of 1139 participants (414 from Fiji; 725 from Samoa) were included in the analyses. Mean salt intake based on 24HUNa was 8.36 g/day (95% CI 8.06–8.66). Mean salt intake estimates from the INTERSALT equations (with and without potassium) were within 1 g/day of the estimate based on 24HUNa, estimates from the Tanaka and Toft equations were 1–2 g/day higher, and estimates from the Kawasaki and Mage equations were > 2 g/day higher (Figure 1). All spot equations correctly classified mean salt intake as above the recommended 5 g/day target. Presence of proportional bias was evident for all equations except for the Kawasaki equation. Estimates from the Tanaka, Toft and INTERSALT equations were higher at lower levels of salt intake and lower at higher levels of salt intake; while the opposite was true for the Mage equation. Subgroup analyses by sex, age group, blood pressure level and timing of spot collection, and sensitivity analyses using various criteria for assessing completeness of urine collection showed results consistent with the main analyses.Conclusion:
The study provides support to the notion that spot urines may be used as an alternative method to estimate population-level salt intake. The INTERSALT equations gave the best estimate of mean salt intake in this population.