Appropriate use of spot-urine sodium estimates for population-level and exploratory analyses: a response to Campbell and Cappuccio

In response to Campbell and Cappuccio's comments, this letter clarifies and defends the appropriate use of spot-urine sodium estimates in population-level and exploratory analyses. The critique misrepresents key aspects of the study design and overstates the limitations of spot-urine equations. While acknowledging that these methods are unsuitable for precise individual assessment, they perform adequately for ranking individuals and examining population-level associations, as supported by extensive validation studies. The reported associations with metabolic traits were internally consistent, biologically plausible, and in agreement with findings from studies using 24-hour urine collections. Dismissing such analyses as "invalid" undermines constructive scientific dialogue and disregards the exploratory value of transparent, hypothesis-generating research.