Spot urine ineffective in predicting sodium excretion
The use of spot urine appears to be unhelpful in estimating 24-hour urinary sodium excretion at the individual level due to its poor performance with regard to misclassification, according to a recent study.
Researchers analysed the relative and absolute differences and misclassification at the individual level from three commonly used methods (Kawasaki; the International Cooperative Study on Salt, Other Factors and Blood Pressure [INTERSALT]; and the Tanaka formulas) for estimating sodium intake among 141 Chinese community residents.
The 24-hour sodium excretion had a mean measurement of 220.8 mmol/day. The median differences between measured sodium and those estimated from the three methods were 6.4 mmol/day (95 percent CI, ‒17.5 to 36.8 mmol/day) for Kawasaki, ‒67.3 mmol/day (‒96.5 to ‒46.9 mmol/day) for INTERSALT and ‒42.9 mmol/day (‒59.1 to ‒24.8 mmol/day) for Tanaka.
The proportions of relative differences >40 percent were 31.2 percent with the Kawasaki method, 41.1 percent with the INTERSALT method and 22.0 percent with the Tanaka method; in about half of the participants, the absolute difference for the three methods was 51.3 mmol/day (3 g salt). The misclassification rates at the individual levels were 63.1, 78.7 and 66.0 percent for the Kawasaka, INTERSALT and Tanaka methods, respectively.
“Evidence for the effect of dietary sodium intake on the risk of cardiovascular disease has been controversial,” researchers said. “One of the main explanations for the conflicting results lies in the great variability associated with measurement methods for sodium intake.”
The collection of spot urine is a convenient method and is frequently used for sodium estimation, they added.