Abstract
We examined the population distribution of urinary sodium concentrations and the validity of existing equations predicting 24-hour sodium excretion from a single spot urine sample among older adults with and without hypertension. In 2013, 24-hour urine collections were obtained from 554 participants in the Multi-Ethnic Study of Atherosclerosis and the Coronary Artery Risk Development in Young Adults study, who were aged 45–79 years and of whom 56% were female, 58% were African American, and 54% had hypertension, in Chicago, Illinois. One-third provided a second 24-hour collection. Four timed (overnight, morning, afternoon, and evening) spot urine specimens and the 24-hour collection were analyzed for sodium and creatinine concentrations. Mean 24-hour sodium excretion was 3,926 (standard deviation (SD), 1,623) mg for white men, 2,480 (SD, 1,079) mg for white women, 3,454 (SD, 1,651) mg for African-American men, and 3,397 (SD, 1,641) mg for African-American women, and did not differ significantly by hypertensive status. Mean bias (difference) in predicting 24-hour sodium excretion from the timed spot urine specimens ranged from −182 (95% confidence interval: −285, −79) to 1,090 (95% confidence interval: 966, 1,213) mg/day overall. Although the Tanaka equation using the evening specimen produced the least bias overall, no single equation worked well across subgroups of sex and race/ethnicity. A single spot urine sample is not a valid indicator of individual sodium intake. New equations are needed to accurately estimate 24-hour sodium excretion for older adults.
Highlights
The gold-standard method of assessment of sodium intake among individuals is derived from measures of 24-hour urinary sodium excretion with multiple samples needed to account for within-individual day-to-day variability [8]; the collection process is burdensome for study participants, resulting in decreased participation and incomplete collection, and it can be expensive for large, population-based studies
We examined the relative validity of existing predictive equations using spot urine sodium concentrations for predicting 24-hour urine sodium excretion in older adults and those with hypertension, and whether the relative validity varied by the timing of the timed spot urine samples
We evaluated the ability of the 4 predictive equations (International Cooperative Study on Salt and Blood Pressure (INTERSALT), Tanaka, Kawasaki, and Mage) (Web Table 2) to estimate population mean levels of 24-hour sodium excretion from single spot urine specimens [25,26,27,28,29]
Summary
It has been estimated that worldwide up to 1.65 million deaths from cardiovascular disease per year can be attributed to excess sodium consumption [7] Many of these studies have relied upon single spot urine samples to represent an individual’s sodium intake despite little validation of these equations and recent work questioning their validity across populations. The goal of the current study was to examine the validity of 4 published predictive equations to determine how well single, timed spot urine specimens can estimate an individual’s 24-hour urinary sodium excretion among African-American and white men and women of older age groups (45–79 years) and those with hypertension.
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