title: Age- and sex-adjusted iodine/creatinine ratio. A new standard in epidemiological surveys? Evaluation of three different estimates of iodine excretion based on casual urine samples and comparison to 24 h values.
abstract: OBJECTIVE
  The most accurate way to measure urinary iodine excretion in epidemiological surveys is still debated. We propose a new principle of estimating iodine excretion based on casual urine samples.
  
  
  METHODS
  A total of 123 24 h urine samples and corresponding casual urine samples were collected from 31 subjects. Iodine excretion was expressed as 24 h iodine excretion and three different estimates: iodine concentration in the casual sample, iodine/gram creatinine in the casual sample, and the new principle-iodine/creatinine ratio in the casual sample, adjusted for expected creatinine excretion of the individual.
  
  
  RESULTS
  All three estimates based on casual urine samples correlated significantly to 24 h values with a r (Pearson) of 0.37 for iodine concentration, 0. 61 for iodine/creatinine ratio and 0.62 for the age- and sex-adjusted iodine/creatinine ratio. The median iodine excretion in the entire group was 143 microg/day in 24 h samples, 87 microg/l as iodine concentration, 77 microg/g creatinine as iodine/creatinine ratio and 126 microg/day as age- and sex-adjusted iodine/creatinine ratio.
  
  
  CONCLUSIONS
  Age- and sex-adjusted iodine/creatinine ratio is a more accurate and unbiased estimate of iodine excretion in epidemiological surveys of adults than the two most frequently used estimated: iodine concentration and iodine/gram creatinine, as these two estimates may introduce a bias depending on the composition of the investigated group. The adjusted iodine/creatinine ratio is superior to the other estimates, especially when individual estimates of 24 h iodine excretion is required or cohorts of selected groups are investigated.
  
  
  BACKGROUND
  This work was supported by grants from the Medical Research Foundation Region Greater Copenhagen, Faroe Islands and Greenland; the Wedell-Wedellsborg Foundation; Musikforlaeggerne Agnes and Knut Morks Foundation.
authors.affiliation: Endocrine Unit, Medical Clinic I, Bispebjerg Hospital, Copenhagen, Denmark. nils.knudsen@dadlnet.dk
authors.forename: N
authors.initials: N
authors.lastname: Knudsen
authors.forename: E
authors.initials: E
authors.lastname: Christiansen
authors.forename: M
authors.initials: M
authors.lastname: Brandt-Christensen
authors.forename: B
authors.initials: B
authors.lastname: Nygaard
authors.forename: H
authors.initials: H
authors.lastname: Perrild
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D003404:Creatinine / Q000652:urine*; D004812:Epidemiologic Methods; D005069:Evaluation Studies as Topic; D005260:Female; D006801:Humans; D007455:Iodine / Q000652:urine*; D008297:Male; D008875:Middle Aged; D012737:Sex Factors
chemical_list: D007455:Iodine; D003404:Creatinine