Observation of serum TSH level after levothyroxine withdrawal in patients with post-ablation differentiated thyroid carcinoma

Objective: To observe the change of serum level of TSH after levothyroxine withdrawal in post-ablation differentiated thyroid carcinoma(DTC) patients. Methods: 145 DTC patients with total or subtotal thyroidectomy who received radioiodine ablation 6 months before were included in this study. For the reason of monitoring of recurrence and metastasis, all the patients were informed levothyroxine withdrawal. The serum level of TSH was measured dynamically once a week after 2 weeks of levothyroxine withdrawal. Among these patients, there were 36 males and 109 females with an average age of 44.72 ± 12.36 years. The patients were classified in to different groups according gender and age. The difference of serum TSH level showed significant if p value was less than 0.05. Results: (1) After 24 weeks of levothyroxine withdrawal, the serum TSH level proved higher in the group of male patients (P = 0.037, 0.006, 0.001), the group of younger patients(P = 0.010, 0.006, 0.001) and the group of follicular thyroid cancer patients (P = 0.483, 0.327, 0.389). (2) After 24 weeks of levothyroxine withdrawal, the percentage of patients whose serum TSH levels were more than 25 μIU/ml was 72.2%, 91.7% and 100% in male patients respectively; 64.2%, 86.2% and 96.3% in female patients individually; 62.1%, 93.1% and 100% in younger patients; 51.7%, 80.5% and 97.7% in elder patients separately. Conclusions: The change of serum TSH level after levothyroxine withdrawal in the post-ablation thyroid carcinoma patients varies with the patients' gender and age. The patients of male and younger ages should be advised to measure the serum TSH level 3 weeks after the levothyroxine withdrawal to avoid the unnecessary high TSH level and the apparent side-effect of hypothyroidism. (authors)