[Should thyroxine treatment be discontinued for four weeks before I(131) thyroid ablation?].

Background: It is a usual practice to discontinue thyroxine treatment for four weeks before (131)I ablation. Symptoms of hypothyroidism usually occur during this time. Use of rhTSH is a helpful alternative in some cases, but problems of availability of this agent during 2012 will limit its use.

Patients And Methods: Plasma TSH and FT4 levels were measured on days 7, 14, 21, and 28 after total thyroidectomy (12 patients) or discontinuation of thyroxine treatment (20 patients). A Mann-Whitney U test was used to compare quantitative variables, and a Chi-square test was used for nominal variables.

Results: On day 14, TSH levels were 30μIU/mL of higher in 71% of patients (66% in the thyroidectomy group and 75% in the group discontinued thyroxine treatment). On day 21, almost all patients from both groups (91% in the thyroidectomy group and 100% in the group discontinued thyroxine treatment) had TSH levels of 30μIU/mL or higher. On day 14, most patients in both groups had FT4 levels below the normal range.

Conclusions: Discontinuation of thyroxine treatment for four weeks is not required. Fourteen days is an adequate time in most patients, and 21 days are sufficient in virtually all patients.