title: Urinary excretion of sodium, potassium, and chloride, but not iodine, varies by timing of collection in a 24-hour calibration study.
abstract: Because of the logistic complexity, excessive respondent burden, and high cost of conducting 24-h urine collections in a national survey, alternative strategies to monitor sodium intake at the population level need to be evaluated. We conducted a calibration study to assess the ability to characterize sodium intake from timed-spot urine samples calibrated to a 24-h urine collection. In this report, we described the overall design and basic results of the study. Adults aged 18-39 y were recruited to collect urine for a 24-h period, placing each void in a separate container. Four timed-spot specimens (morning, afternoon, evening, and overnight) and the 24-h collection were analyzed for sodium, potassium, chloride, creatinine, and iodine. Of 481 eligible persons, 407 (54% female, 48% black) completed a 24-h urine collection. A subsample (n = 133) collected a second 24-h urine 4-11 d later. Mean sodium excretion was 3.54 ± 1.51 g/d for males and 3.09 ± 1.26 g/d for females. Sensitivity analysis excluding those who did not meet the expected creatinine excretion criterion showed the same results. Day-to-day variability for sodium, potassium, chloride, and iodine was observed among those collecting two 24-h urine samples (CV = 16-29% for 24-h urine samples and 21-41% for timed-spot specimens). Among all race-gender groups, overnight specimens had larger volumes (P < 0.01) and lower sodium (P < 0.01 to P = 0.26), potassium (P < 0.01), and chloride (P < 0.01) concentrations compared with other timed-spot urine samples, although the differences were not always significant. Urine creatinine and iodine concentrations did not differ by the timing of collection. The observed day-to-day and diurnal variations in sodium excretion illustrate the importance of accounting for these factors when developing calibration equations from this study.
authors.affiliation: Division of Health and Nutrition Examination Surveys, National Center for Health Statistics, Centers for Disease Control and Prevention, Hyattsville, MD, USA. cwang@cdc.gov
authors.forename: Chia-Yih
authors.initials: CY
authors.lastname: Wang
authors.forename: Mary E
authors.initials: ME
authors.lastname: Cogswell
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Loria
authors.forename: Te-Ching
authors.initials: TC
authors.lastname: Chen
authors.forename: Christine M
authors.initials: CM
authors.lastname: Pfeiffer
authors.forename: Christine A
authors.initials: CA
authors.lastname: Swanson
authors.forename: Kathleen L
authors.initials: KL
authors.lastname: Caldwell
authors.forename: Cria G
authors.initials: CG
authors.lastname: Perrine
authors.forename: Alicia L
authors.initials: AL
authors.lastname: Carriquiry
authors.forename: Kiang
authors.initials: K
authors.lastname: Liu
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Sempos
authors.forename: Cathleen D
authors.initials: CD
authors.lastname: Gillespie
authors.forename: Vicki L
authors.initials: VL
authors.lastname: Burt
mesh_terms: D000293:Adolescent; D000328:Adult; D002138:Calibration; D002712:Chlorides / Q000652:urine*; D002940:Circadian Rhythm; D003404:Creatinine / Q000652:urine; D003430:Cross-Sectional Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007455:Iodine / Q000652:urine*; D008297:Male; D009749:Nutrition Surveys; D011188:Potassium / Q000652:urine*; D012964:Sodium / Q000652:urine*; D011795:Surveys and Questionnaires; D013997:Time Factors; D059349:Urine Specimen Collection; D055815:Young Adult
chemical_list: D002712:Chlorides; D007455:Iodine; D012964:Sodium; D003404:Creatinine; D011188:Potassium