n :  the amount of iodine expressed in micrograms per 100 milliliters of blood serum that is precipitated with serum proteins and that serves as a measure of the activity of the thyroid gland <the protein-bound iodine in the normal human being ranges from 4 to 8 micrograms, in hypothyroidism falls below this range, and in hyperthyroidism rises above it>  .
 
 
 
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