The urinary iodide level of a population is the indicator of its iodine nutrition status. The WHO has set the target for population urinary iodide at 100-300 parts per billion (ppb). Measuring such low levels of iodine is challenging and there are no commercially available field screening methods; samples must be sent for laboratory analysis. Our goal was to translate the Sandell-Kolthoff kinetic assay for urinary iodide to a paper test card format.
The specific aim was to distinguish between inadequate (<100 ppb), adequate (100-300 ppb), and over-iodized (>300 ppb) samples of simulated urine under field conditions using the paper card. We designed a field test kit with reagents and paper test cards printed with wax to delineate reaction areas. To validate the kit, two analysts independently tested the same 30 solutions. The solutions were created in a simulated urine matrix and spiked with iodide to physiologically relevant concentrations. The cards were categorized by eye, and pictures of the test cards were analyzed with a computer program to estimate the sample concentrations.
93% of samples were correctly categorized based on visual estimation. Software analysis predicted the populationâs average as 195 ppb iodide. The true value was 225 ppb iodide; therefore, the cards correctly predicted the populationâs health status. Individual samples had errors of 61 ± 23 ppb iodide.
The Sandell-Kolthoff reaction has been adapted into a portable format that can accurately categorize physiologically relevant iodide concentrations and should be further developed for urine.