title: Intraindividual variation in urinary iodine concentrations: effect of adjustment on population distribution using two and three repeated spot urine collections.
abstract: OBJECTIVE
  To determine the effect of adjustment for intraindividual variation on estimations of urinary iodine concentrations (UIC), prevalence of iodine deficiency and population distribution of iodine status.
  
  
  METHODS
  Community-dwelling older adults from New South Wales, Australia.
  
  
  METHODS
  84 healthy men and women aged 60-95 years were recruited prior to introduction of the mandatory iodine fortification programme.
  
  
  METHODS
  UIC data were collected from three spot urine samples, each 1 week apart. Repeated measures analysis of variance were determined between-person (sb) and total (sobs) SDs. Adjusted UIC values were calculated as ((person's UIC-group mean)×(sb/sobs))+group mean, and a corrected UIC distribution was calculated.
  
  
  RESULTS
  The sb/sobs for using three samples and two samples were 0.83 and 0.79, respectively. Following adjustment for intraindividual variation, the proportion with UIC <50 μg/L reduced from 33% to 19%, while the proportion with UIC ≥100 μg/L changed from 21% to 17%. The 95th centile for UIC decreased from 176 to 136 μg/L. Adjustment by taking averages yielded a lesser degree of contraction in the distribution than the analysis of variance method.
  
  
  CONCLUSIONS
  The addition of information about intraindividual variability has potential for increasing the interpretability of UIC data collected to monitor the iodine status of a population.
authors.affiliation: School of Medicine, Faculty of Science, Medicine and Health, University of Wollongong, Wollongong, New South Wales, Australia.
authors.forename: Karen E
authors.initials: KE
authors.lastname: Charlton
authors.forename: Marijka J
authors.initials: MJ
authors.lastname: Batterham
authors.forename: Li Min
authors.initials: LM
authors.lastname: Buchanan
authors.forename: Dorothy
authors.initials: D
authors.lastname: Mackerras
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D003710:Demography; D005260:Female; D006801:Humans; D007455:Iodine / Q000652:urine*; D008297:Male; D008875:Middle Aged; D059349:Urine Specimen Collection / Q000379:methods / Q000706:statistics & numerical data
chemical_list: D007455:Iodine
keywords: EPIDEMIOLOGY; NUTRITION & DIETETICS; PRIMARY CARE; PUBLIC HEALTH