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

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 (s b ) and total (s obs ) SDs. Adjusted UIC values were calculated as ((person9s UIC−group mean)×(s b /s obs ))+group mean, and a corrected UIC distribution was calculated. Results The s b /s obs for using three samples and two samples were 0.83 and 0.79, respectively. Following adjustment for intraindividual variation, the proportion with UIC 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.