... measurement of 3',5'-diiodothyronine ((3',5'-T2) in unextracted serum. Interference in binding of radioactive 3',5'-T2 to anti ... , and 0.22%, respectively. 3'-Monoiodothyronine cross-reacted 1.7%. Serum 3',5'-T2 concentrations were (mean +/- SD) 6.4 +/- 2 ... did not differ significantly from normal at a time when serum T4 and T3 were clearly elevated. Oral administration of 300 ...