Objective:
High dietary sodium (Na) and low dietary potassium (K) intakes are associated with adverse blood pressure levels and excess risks of cardiovascular diseases. The Sodium/potassium (Na/K) ratio is a composite index of Na and K. Recently, we found Na/K ratio of casual urine is useful for estimating 24-h urinary Na/K ratio in healthy Japanese participants. However, this finding has not been validated in different ethnic groups. Our aim was to assess the utility across and within populations of casual (spot) urine specimens to estimate 24-h urinary Na/K ratio using data from the International Cooperative Study on Salt, Other Factors, and Blood Pressure (INTERSALT).
Methods:
The INTERSALT study collected standardized data on casual urinary Na and K concentrations, and also on timed 24-h urinary Na and K excretion for 10,079 men and women ages 20-59 years from 52 population samples in 32 countries. Pearson correlation coefficients and agreement quality analysis (by the Bland-Altman method) were computed for Na/K ratio of casual urine against 24-h urinary Na/K ratio.
Results:
Overall mean value of Na/K ratio in 24-h urine collections was 3.24. 24-h urinary Na/K ratio and Na/K ratio of casual urine across the 52 population samples were highly correlated: r=0.96 (overall), r=0.96 (men), r=0.95 (women), r=0.94 (ages 20-29), r=0.94 (ages 30-39), r=0.95 (ages 40-49) and r=0.95 (ages 50-59). 24-hour urinary Na/K ratio and Na/K of casual urine across the 10,079 individuals had moderately strong correlations: r=0.69 (overall), r=0.70 (men), r=0.68 (women), r=0.58 (white), r=0.47 (black), r=0.81 (Amerindian), r=0.70 (Asian Indian), r=0.64 (east-Asian), r=0.70 (other ethnicities), r=0.58 (with anti-hypertensive medication use) and r=0.72 (without anti-hypertensive medication use). The bias estimate with the Bland-Altman method, defined as the difference between Na/K of 24-h urine collection and casual urine, was approximately 0.4 across both populations and individuals, independent of age, gender and anti-hypertensive medication use across the 52 population samples. Bias estimates across population samples were 0.39 (overall), 0.42 (men), 0.36 (women), 0.32 (ages 20-29), 0.41 (ages 30-39), 0.37 (ages 40-49) and 0.46 (ages 50-59). Bias estimates for the 10,079 individuals were 0.40 (overall), 0.42 (men), 0.37 (women), 0.33 (white), 0.69 (black), 0.04 (Amerindian), 0.22 (Asian Indian), 0.65 (east-Asian), 0.31 (other ethnicities), 0.45 (with anti-hypertensive medication use) and 0.38 (without anti-hypertensive medication use).
Conclusions:
These findings indicate that casual urine Na/K ratio is a useful, low-burden, low-cost method alternative to 24-h urine collection for estimation of urinary Na/K ratio across populations of various ethnicities. It is also applicable to individual urinary Na/K ratio.
Response to “Letter to the Editor regarding the report entitled Urinary sodium/potassium ratio as a screening tool for hyperaldosteronism in men with hypertension”
