Feasibility of collecting 24-h urine to monitor sodium intake in the National Health and Nutrition Examination Survey

Abstract

Background: Twenty-four-hour urine sodium excretion is recommended for monitoring population sodium intake. Because of concerns about participation and completion, sodium excretion has not been collected previously in US nationally representative surveys.

Objective: We assessed the feasibility of implementing 24-h urine collections as part of a nationally representative survey.

Design: We selected a random half sample of nonpregnant US adults aged 20-69 y in 3 geographic locations of the 2013 NHANES. Participants received explicit instructions, started and ended the urine collection in a urine study mobile examination center, and answered questions about their collection. Among those with a complete 24-h urine collection, a random one-half were asked to collect a second 24-h urine sample. Sodium, potassium, chloride, and creatinine excretion were analyzed.

Results: The final NHANES examination response rate for adults aged 20-69 y in these 3 study locations was 71%. Of those examined (n = 476), 282 (59%) were randomly selected to participate in the 24-h urine collection. Of these, 212 persons [75% of those selected for 24-h urine collection; 53% (equal to 71% × 75% of those selected for the NHANES)] collected a complete initial 24-h specimen and 92 persons (85% of 108 selected) collected a second complete 24-h urine sample. More men than women completed an initial collection (P = 0.04); otherwise, completion did not vary by sociodemographic characteristics, body mass index, education, or employment status for either collection. Mean 24-h urine volume and sodium excretion were 1964 ± 1228 mL and 3657 ± 2003 mg, respectively, for the first 24-h urine sample, and 2048 ± 1288 mL and 3773 ± 1891 mg, respectively, for the second collection.

Conclusion: Given the 53% final component response rate and 75% completion rate, 24-h urine collections were deemed feasible and implemented in the NHANES 2014 on a subsample of adults aged 20-69 y to assess population sodium intake. This study was registered at clinicaltrials.gov as NCT02723682.

Keywords: 24-hour urine; NHANES; biomarker; hypertension; sodium excretion; sodium intake.

© 2016 American Society for Nutrition.

Figures

FIGURE 1

Participation protocol for the NHANES 24-h urine collection feasibility study in adults aged 20–69 y. MEC, mobile examination center; UMEC, urine study mobile examination center.

FIGURE 2

Completion rates for the NHANES postexamination components PAM and second DR in participants aged 20–69 y by eligibility for the 24-h urine collection feasibility study. Participants selected to collect a 24-h urine sample had significantly higher completion rates for the PAM than did those not selected, *P < 0.05 (chi-square test). No significant differences in DR completion rate were observed between participants selected for 24-h urine collection and those not selected. DR, dietary recall; PAM, physical activity monitor.

FIGURE 3

Adjusted mean (95% CI) 24-h urine volume for adults aged 20–69 y in the NHANES 24-h urine collection feasibility study with a complete specimen, by sex and race. Mean volume is adjusted for duration of collection. One participant was excluded from the initial 24-h urinary analysis because the total urine volume was unknown. The number of complete specimens for the first 24-h urine collection was as follows: total, n = 211; men, n = 112; women, n = 99; non-Hispanic blacks, n = 64; and non-Hispanic whites, n = 130. The number of complete specimens for the second 24-h urine collection was as follows: total, n = 92; men, n = 47; women, n = 45; non-Hispanic blacks, n = 28; and non-Hispanic whites, n = 55. The “total” category includes race and ethnicity groups other than non-Hispanic black or non-Hispanic white. Significant difference in mean urine volume observed between non-Hispanic black and non-Hispanic white participants for both first and second 24-h urine collection, *P < 0.05 (t test). NHB, non-Hispanic black; NHW, non-Hispanic white.

FIGURE 4

Mean (95% CI) total 24-h urine sodium (A), potassium (B), chloride (C), and creatinine (D) for adults aged 20–69 y in the NHANES 24-h urine collection feasibility study with a complete urine specimen, by sex and race. One participant was excluded from the initial 24-h urinary analysis because the total urine volume was unknown. The number of complete specimens for the first 24-h urine collection was as follows: total, n = 211; men, n = 112; women, n = 99; non-Hispanic blacks, n = 64; and non-Hispanic whites, n = 130. The number of complete specimens for the second 24-h urine collection was as follows: total, n = 92; men, n = 47; women, n = 45; non-Hispanic blacks, n = 28; and non-Hispanic whites, n = 55. The “total” category includes other race and ethnicity groups. Mean 24-h sodium, potassium, chloride, and creatinine excretions were significantly higher in men than in women, *P < 0.05 (t test), but did not differ by race, for both the first and second urine collections. NHB, non-Hispanic black; NHW, non-Hispanic white.