Endocrine Abstracts

Background and Aim: RAIT has a high success rate in achieving cure of hyperthyroidism but there is unpredictability of thyroid status during the initial post-RAI period, making it difficult to counsel patients or plan medical therapy. We assessed the role of updated TRAB level at the time of RAIT in predicting persistent post-RAI hyperthyroidism.

Patients and Methods: We measured TRAB at the time of RAIT (fixed 550MBq dose) in 26 patients with Graves’ disease. Patients were followed-up at 6, 12, 24 weeks and as required. Post-RAI antithyroid agents were started only if required. We recorded demographic data, thyroid function and antithyroid agent use at each visit. Thyroid status was correlated to age, gender, T4 at diagnosis and TRAB at RAIT.

Results: 20% males, mean age 49 years; T4 and TRAB at diagnosis and at RAIT were 33 pmo/l, 15 pmo/l, 10 IU/l and 9.4IU/l respectively. Patients with persistent post-RAIT hyperthyroidism had a significantly higher mean TRAB at RAIT as compared to those who were not hyperthyroid at 6 and 12 weeks (23.4 v 4.3 IU/l and 17.1 v 7.1IU/l; P<0.05, respectively) and patients with TRAB >6IU/l were more likely to be hyperthyroidism at this stage (chi square; P<0.05). Patients who were hyperthyroid at 24 weeks requiring a second dose also had a higher mean TRAB (12.7 v 8.6IU/l), but this was not statistically significant.

Conclusions: TRAB of >6IU/l at the time of RAIT allows us to predict persistent hyperthyroidism until 4 months post-RAI and may prompt clinicians to start proactive antithyroid therapy. We also believe that with the inclusion of higher number of patients we would be able to predict hyperthyroidism at 6 months and early consideration of second dose of RAIT. Untreated T4 level at diagnosis is also predictive but is often not available at the time of RAIT