Intraindividual variation in urinary iodine concentrations: Effect of adjustment on population distribution using two and three repeated spot urine collections

Karen Charlton, Marijka Batterham, Li Min Buchanan, Dorothy Mackerras

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Abstract

Objectives: 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.

Setting: 
Community-dwelling older adults from New South Wales, Australia.

Participants: 
84 healthy men and women aged 60–95 years were recruited prior to introduction of the mandatory iodine fortification programme.

Primary and secondary outcome measures:
 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.
Original languageEnglish
Article numbere003799
Pages (from-to)1-5
Number of pages5
JournalBMJ Open
Volume4
DOIs
Publication statusPublished - 2014

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