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

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.

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.

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.

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.