Restricted intraindividual urinary iodine concentration variability in nonfasting subjects

Objective: Individual urinary iodine concentration (UIC) reflects iodine intake over a short time prior to sampling. Since eating habits are relatively constant in single subjects, UIC should be relatively constant in a given individual. The aim of our study was to verify this hypothesis by assessing UIC in repeated single urine samples from a group of healthy subjects. Design and Setting: A prospective sequential investigation was performed in 131 volunteer health workers or students recruited in our University hospital. Interventions: Single urine samples were taken in a nonfasting state, between 0900 and 1100 hours. Group 1 was composed by 131 subjects who collected one urine sample. Group 2 was composed by 11 subjects of the group 1, who collected multiple repeated urine samples ( as a whole 158 urine samples, mean 14 samples each). UIC mean +/- s. d., median and coefficient of variation (CV%) was measured in both groups. Results: Interindividual UIC variation was wide, UIC ranging from 21 to 382 mu g/l, mean 136 +/- 84 mu g/ l, median 124 mu g/ l, CV 62%. Also in the 11 subjects repeatedly sampling there were considerable differences among individual UIC average levels ( ranging from 37 +/- 15 to 221 +/- 91 mu g/ l). However, in this second group, the intraindividual variation was considerably restricted ( CV% 36). Conclusions: The present study shows that in a nonfasting state in mid-morning UIC is more stable from day to day in a single subject, depending on his eating habits, than in various subjects. Thus, a single urine sample even in nonfasting state may give some rough information about the individual's iodine status.