Aetiological sub-classification of thyrotoxicosis and relevance of TT3/TT4 ratio in sub-classification of patients with thyrotoxicosis: an Indian cross-sectional study

Background: Thyrotoxicosis is a common endocrine problem. Sub-classification and rapid diagnosis of disease is crucial in the management. Methods: In this prospective cross-sectional study from India, newly diagnosed thyrotoxicosis patients were enrolled. All patients were sub classified into Graves’ disease, (GD), sub-acute thyroiditis (SAT) and toxic nodular goiter (TNG) based on diagnostic criteria. Clinical features were noted and TT3, TT4 and TSH level were measured.  A thyroid scan was also done. Results: TNG, respectively. Mean± SD age for GD, SAT and TNG were 36.88±10.55, 37.44±5.96 and 61±11.36 years, respectively. Most of patients were female (77.63%). Goiter was present in 81.25%, 55.56% and 100% of GD, SAT and TNG patients respectively. Mean TT3/TT4 ratio was higher (20.15±5.45 verses 12.72±0.77) in GD as compared to SAT patients. The area under ROC curve of the TT3/TT4 for diagnosis of GD was 0.964. Cut off level of TT3/TT4 ratio >14.1 offered best sensitivity, specificity, PPV (positive predictive value) and accuracy. Conclusions: This first report from India on sub-classification of thyrotoxicosis shows that GD is the commonest cause of thyrotoxicosis. TT3/TT4 ratio of >14.1 may help in differentiating the cause of thyrotoxicosis.