Comparison of Population Iodine Estimates from 24-Hour Urine and Timed-Spot Urine Samples

Abstract

Estimates of UIC, I/Cr, and estimated 24-hour UIE (I/Cr × predicted 24-hour Cr) from spot urine samples should not be used interchangeably. Estimated 24-hour UIE, where predicted 24-hour Cr varies by age, sex, ethnicity, and anthropometric measures and was calculated with prediction equations using data from the sample, was more comparable to observed 24-hour UIE than when predicted 24-hour Cr was from published estimates from a different population. However, currently no cutoffs exist to interpret population estimated 24-hour UIE values.

Urinary 24-h creatinine excretion in adults and its use as a simple tool for the estimation of daily urinary analyte excretion from analyte/creatinine ratios in populations

“…Meanwhile, for adults, various creatinine adjustment approaches have been suggested and applied with quite varying results regarding the assessment of their applicability. [11][12][13] In children, anthropometry-based (i.e. body weight-corrected) age-and sex-specific creatinine reference values to estimate 24-h analyte excretion rates have been shown to generate valid estimates, 5,14-17 despite body composition varies highly, especially during growth in children and adolescents.…”

Iodine status of Queensland children and the associations with diet and thyroid function

“…Urinary iodine is usually expressed as; 1) median urinary iodine concentration or UIC (ug/L) (usually from first morning void urine samples), 2) urinary iodine excretion or UIE from 24 hour urine samples (ug/24-h or ug/day) or 24hr excretion (UIE), or 3) an iodine creatinine ratio (I/Cr x predicted 24hr urine output) (1,44,45). Throughout iodine literature UIC and UIE are used interchangeable, despite the expressions representing different estimates of iodine (44,45).…”

“…Throughout iodine literature UIC and UIE are used interchangeable, despite the expressions representing different estimates of iodine (44,45). The WHO states that provided a sufficient number of spot urine samples are collected from the population, the added burden of collecting 24hr urine samples, especially from young children, is not necessary (1).…”

“…The WHO states that provided a sufficient number of spot urine samples are collected from the population, the added burden of collecting 24hr urine samples, especially from young children, is not necessary (1). Furthermore, there is no validated criterion for appropriate cutoffs describing the varying degrees of iodine status using UIE or I/Cr as an expression, as the estimate can vary between ages, genders and ethnicity (44,45). As UIC is largely influenced by urine volume, which is known to vary day to day, but adjusting for the protein creatinine …”

“…(Cr) (product of muscle metabolism) can reduce the impact of this variation on the interpretation of iodine nutrition (20,44,45). The challenge in correcting for creatinine is that it is influenced by BMI, age, gender and ethnicity and has no validated cut-off criteria for iodine nutrition (20,46).…”