Several investigations have reported an increase, in stored serum, in apparent thyroxine (T4) concentration measured by competitive binding radioassay (CPBR) with thyroxine-binding globulin (TBG) as the binding reagent [l-7]. Watson and Lees [4] attributed this increase to the production of a “mimic T4” during storage. Recently, we [6] and Rootwelt [7], working independently, discovered that th...
