¹²³I Thyroid Uptake and Thyroid Size at 24, 48, and 72 Hours after the Administration of Recombinant Human Thyroid-Stimulating Hormone to Normal Volunteers

CONTEXT: Recombinant human TSH (rhTSH) is used to evaluate thyroid carcinoma patients and off-label for (131)I thyroid ablation and nontoxic goiter therapy. OBJECTIVE: Our objective was to determine the optimal time for (131)I administration after rhTSH. PARTICIPANTS: Twenty-five euthyroid nongoitrous volunteers participated in the study. DESIGN: Baseline 24-h thyroid (123)I uptake (RAIU) was measured, and then 0.1 mg rhTSH was administered. (123)I was administered 24, 48, or 72 h after rhTSH, and a repeat 24-h RAIU was obtained. SETTING: The study was conducted at an academic research center. MAIN OUTCOME MEASURES: Thyroid function tests, thyroid ultrasounds, and electrocardiograms were measured before rhTSH, then daily for 4 d, and finally 7 d after rhTSH. RESULTS: Serum TSH concentrations 24 h after rhTSH increased from 1.7 +/- 0.5 muU/ml (mean +/- sd) to 13.3 +/- 4. The 24-h RAIUs rose from 25 +/- 5 to 47 +/- 8% (88% increase) when the (123)I was given at 24 h after rhTSH and from 29.8 +/- 7 to 40.5 +/- 13% (36% increase) when the (123)I was given at 48 h and were unchanged when the (123)I was given at 72 h. The post-rhTSH RAIU increase was greater at 24 than at 72 h (P < 0.005) and marginally greater than at 48 h (P = 0.057). Thyroid volumes significantly increased 48 h after rhTSH (10 +/- 3.8 vs. 11.1 +/- 3.7 ml; P < 0.009). Electrocardiograms were normal. CONCLUSIONS: Marked increases in RAIU occurred when (123)I was given 24 h after rhTSH administration to euthyroid volunteers. Smaller increases were observed at 48 h and none at 72 h.