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.
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.
Knudsen
N
N
Endocrine Unit, Medical Clinic I, Bispebjerg Hospital, Copenhagen, Denmark. nils.knudsen@dadlnet.dk
Christiansen
E
E
Brandt-Christensen
M
M
Nygaard
B
B
Perrild
H
H
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
D007455:Iodine; D003404:Creatinine