Development of a routine 125I bioassay program for athyrotic individuals using a pseudo uptake retention function.

Individuals working in iodine production require bioassay to determine if intakes have occurred. This is both to determine dose received for regulatory purposes and to verify whether workplace controls limiting the spread of contamination are adequate. Thyroid monitoring is commonly used as a bioassay technique to detect isotopes of iodine. If an individual performing iodine processing does not have a thyroid gland, other means must be used to determine intake and infer dose. Data was obtained from a previously published thesis that attempted to verify a model for absorption and retention of iodine by athyrotic individuals. These data were reevaluated to determine a pseudo uptake retention function. This analysis does not attempt to identify a biokinetic model, only to describe excretion of iodine and calculate an intake. Once the pseudo uptake retention function was derived, it was combined with the standard respiratory and gastrointestinal tract models as an inhalation intake retention function. A periodic urine bioassay protocol has been designed using the intake retention function described above and a conservative dose coefficient derived using organ dose coefficients for reference man, excluding the thyroid, and the appropriate weighting factors.