Serum triiodothyronine (T3) and thyroxine (T4) were measured in thirteen unselected hyperthyroid patients before and at frequent intervals after iodine-131 treatment. There was an abrupt rise in T3 from a pretreatment mean of 250 ng/100 ml to a maximum of 365 ng/100 ml at 24 hours. Total T4 rose from a mean of 18·7 μg/100 ml to a maximum of 22·3 μg/100 ml at 24-48 hours. These findings may explain why an occasional patient develops acute thyroid crisis after radioiodine treatment.
Bibliographical noteFunding Information:
Sfstance, Dr D. Burnett, of the Clinical Biochemistry Department, St. Albans, for measurement of phenytoin levels, and the National Fund for Research into Crippling Diseases for financial support.
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