T3 uptake test in familial dysalbuminemic hyperthroxinemia

The labeled T3 (*T3) binds normally to available binding sites on TBG, but cannot bind to available sites on the abnormal albumin; as a result, the amount left over to bind to the resin (or other binder such as talc or dextran-coated charcoal) is normal. The serum total T4 is high due to excess binding to the abnormal albumin, the T3-uptake and THBR are normal, and the serum free T4 index is high.