Aim: To determine whether the ratio of T3 to TRAB (TSH Receptor Antibody levels) could be used to identify those patients with Graves thyrotoxicosis who cannot be controlled with antithyroid drug (ATD) therapy and those who will relapse within 2 years of discontinuation of ATD therapy.
Method: Retrospective analysis of 22 patients with Graves disease and their relapse at 2 years after discontinuation of ATD therapy. Patients were diagnosed with Graves thyrotoxicosis on the basis of raised Free T3 levels with associated suppressed TSH and positive TRAB level. Initial Free T3:TRAB ratios were calculated.
Results: Of 22 patients with Graves disease (4 males), 7 were not controlled on ATD and needed definitive therapy. Ten relapsed within 2 years of stopping ATD therapy (mean time to relapse 11.8 months, range 321 months). Five patients had not relapsed within 2 years of stopping ATD therapy. Mean length of ATD treatment was 16 months (range 12 to 24 months). Patients who were not controlled on ATD therapy had a mean T3:TRAB ratio of 1(median 0.75). Those who relapsed within 2 years after discontinuation of ATD therapy had a mean T3:TRAB ratio of 3.5 (median 2.3). Patients who did not relapse within 2 years had a mean T3:TRAB ratio of 5 (median 5.1).
Conclusion: Predicting the course of Graves thyrotoxicosis is difficult. Low T3:TRAB ratios at the time of diagnosis of Graves disease can predict those patients who will not be controlled on antithyroid drug therapy alone and so prompt the need for early referral for Radioactive Iodine or surgery. High T3:TRAB ratios at the time of diagnosis can predict those patients who will not relapse within 2 years of discontinuation of ATD therapy.