title: Estimating the population distribution of usual 24-hour sodium excretion from timed urine void specimens using a statistical approach accounting for correlated measurement errors.
abstract: BACKGROUND
  High US sodium intake and national reduction efforts necessitate developing a feasible and valid monitoring method across the distribution of low-to-high sodium intake.
  
  
  OBJECTIVE
  We examined a statistical approach using timed urine voids to estimate the population distribution of usual 24-h sodium excretion.
  
  
  METHODS
  A sample of 407 adults, aged 18-39 y (54% female, 48% black), collected each void in a separate container for 24 h; 133 repeated the procedure 4-11 d later. Four timed voids (morning, afternoon, evening, overnight) were selected from each 24-h collection. We developed gender-specific equations to calibrate total sodium excreted in each of the one-void (e.g., morning) and combined two-void (e.g., morning + afternoon) urines to 24-h sodium excretion. The calibrated sodium excretions were used to estimate the population distribution of usual 24-h sodium excretion. Participants were then randomly assigned to modeling (n = 160) or validation (n = 247) groups to examine the bias in estimated population percentiles.
  
  
  RESULTS
  Median bias in predicting selected percentiles (5th, 25th, 50th, 75th, 95th) of usual 24-h sodium excretion with one-void urines ranged from -367 to 284 mg (-7.7 to 12.2% of the observed usual excretions) for men and -604 to 486 mg (-14.6 to 23.7%) for women, and with two-void urines from -338 to 263 mg (-6.9 to 10.4%) and -166 to 153 mg (-4.1 to 8.1%), respectively. Four of the 6 two-void urine combinations produced no significant bias in predicting selected percentiles.
  
  
  CONCLUSIONS
  Our approach to estimate the population usual 24-h sodium excretion, which uses calibrated timed-void sodium to account for day-to-day variation and covariance between measurement errors, produced percentile estimates with relatively low biases across low-to-high sodium excretions. This may provide a low-burden, low-cost alternative to 24-h collections in monitoring population sodium intake among healthy young adults and merits further investigation in other population subgroups.
authors.affiliation: Division of Health and Nutrition Examination Surveys, National Center for Health Statistics, CDC, Hyattsville, MD; cwang@cdc.gov.
authors.forename: Chia-Yih
authors.initials: CY
authors.lastname: Wang
authors.affiliation: Department of Statistics, Iowa State University, Ames, IA;
authors.forename: Alicia L
authors.initials: AL
authors.lastname: Carriquiry
authors.affiliation: Division of Health and Nutrition Examination Surveys, National Center for Health Statistics, CDC, Hyattsville, MD;
authors.forename: Te-Ching
authors.initials: TC
authors.lastname: Chen
authors.affiliation: National Heart, Lung, and Blood Institute, and.
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Loria
authors.affiliation: Division of Laboratory Sciences, National Center for Environmental Health.
authors.forename: Christine M
authors.initials: CM
authors.lastname: Pfeiffer
authors.affiliation: Department of Preventive Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL.
authors.forename: Kiang
authors.initials: K
authors.lastname: Liu
authors.affiliation: Office of Dietary Supplements, NIH, Bethesda, MD;
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Sempos
authors.affiliation: Division of Nutrition, Physical Activity, and Obesity, and.
authors.forename: Cria G
authors.initials: CG
authors.lastname: Perrine
authors.affiliation: Division for Heart Disease and Stroke Prevention, National Center for Chronic Disease Prevention and Health Promotion, CDC, Atlanta, GA; and.
authors.forename: Mary E
authors.initials: ME
authors.lastname: Cogswell
mesh_terms: D000293:Adolescent; D000328:Adult; D000465:Algorithms; D002138:Calibration; D002940:Circadian Rhythm; D004219:District of Columbia; D005260:Female; D006801:Humans; D008297:Male; D008954:Models, Biological; D015596:Nutrition Assessment; D009749:Nutrition Surveys / Q000379:methods*; D065667:Renal Elimination; D015203:Reproducibility of Results; D012727:Sex Characteristics; D012964:Sodium / Q000652:urine*; D012982:Sodium, Dietary / Q000008:administration & dosage* / Q000378:metabolism; D014504:Urban Health; D055815:Young Adult
chemical_list: D012982:Sodium, Dietary; D012964:Sodium
keywords: 24-hour urine collection; calibration; nutrition survey; population distribution; sodium; timed urine void; usual sodium intake
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