Endocrine Abstracts

The factors influencing the final outcomes of ¹³¹I therapy are indefinitely known, besides its practical use since more than 60 years. One of the considered factors affecting the results of ¹³¹I therapy is iodine metabolism.

Aim: The aim of the study was the evaluation of the iodine uptake and the effective half-life of ¹³¹I influence on the result of radioactive iodine therapy in patients treated due to Graves’ hyperthyroidism.

Material and methods: A hundred subjects (84 females and 16 males) aged 27–76 with diagnosed Graves’ disease, were enrolled. In all patients, the thyroid technetium-99m scan and determination of the serum levels of FT3, FT4, TSH, TSHRAb were performed. Iodine uptake was measured at 24 h, 48 h, then the half-life has been determined. The therapeutic activity of ¹³¹I was calculated according to Marinelli formula. After the 12th months follow up period, the thyroid function has been estimated.

Results: The levels of thyroid hormones and TSH before therapy were: FT3 5.7–74.8 pmol/l, FT4 10.3–90 pmol/l, TSH 0.02–0.08 mIU/l.

After 24 h, radioiodine uptake ranged between 18 and 89%, but after 48 h between 17 and 83%. The effective half-life range was from 1.2 to 8.1days.

The administered therapeutic activities ranged between 148 and 1113.7 MBq.

After 1 year follow-up, the effective ¹³¹I therapy was confirmed in 60 patients (29 euthyreosis, 31 hypothyreosis), but in 40 patients hyperthyreosis still remained.

Statistical analysis revealed no correlations between 24-h and 48-h radioiodine uptake as well as T1/2 and the result of ¹³¹I therapy.

Conclusions: The iodine uptake as well as the effective half-life of ¹³¹I did not influence the result of ¹³¹I therapy.