The purpose of this retrospective study was to clarify the possible risk factors of early hypothyroidism after RAI therapy in Graves' disease.

Hyperthyroidism is a clinical syndrome caused by increased thyroid hormone in the blood, it can lead to multiple complications, including cardiac, hepatic, and hematologic system complications. More than 80% of hyperthyroidism are caused by Graves' disease (GD). 3% of women and 0.5% of men may suffer GD in their lifetime [1].

Radioactive iodine (RAI) therapy is an important treatment option for Graves' disease (GD), the main side effect of RAI treatment is hypothyroidism, and the factors resulting in hypothyroidism are still controversial [2]. Male gender, smaller thyroid weight, higher thyroid-stimulating hormone, and smaller thyroid volume are Suggested to be the main risk factors for early hypothyroidism [2]-[3].

Inclusion Criteria:

1. Graves' disease patients after one year of RAI therapy .
2. Suppressed serum thyrotropin (TSH) <0.55 µU/ml , elevated serum free triiodothyronine (FT3) > 6.5 pmol/L , free thyroxin FT4 >22.7 pmol/L .

Exclusion Criteria:

1. Patients with other causes of hyperthyroidism , such as toxic multinodular goiter and single toxic adenoma
2. Thyroid cancer
3. Recurrent GD
4. Previous Thyroid surgery
5. Patients can't complete the follow -up within 6 months.

All thyrotoxic patients treated with RAI