Role of triiodothyronine in hypothyroidism: Consensus statement from the Indian Thyroid Society

ABSTRACT Hypothyroidism is a chronic endocrine disorder resulting from the deficiency of thyroid hormones, thyroxine (T4) and triiodothyronine (T3). Globally, its prevalence is gradually increasing, affecting up to 5% of the general population, with an additional 5% estimated to remain undiagnosed. In India, the prevalence of hypothyroidism is more than twice that reported in Western countries. A large cross-sectional Indian study reported an overall prevalence of 10.95%, with 8.02% of patients having subclinical hypothyroidism. The clinical manifestations are diverse and often nonspecific, including fatigue, weight gain, depression, poor concentration, and menstrual irregularities. If untreated, hypothyroidism can lead to cardiovascular disease and increased mortality. Levothyroxine (LT4) monotherapy remains the cornerstone of treatment, aimed at restoring euthyroidism and alleviating symptoms. However, nearly one-third of patients continue to experience residual symptoms despite achieving biochemical targets, raising interest in combination therapy with LT4 and liothyronine (LT3). In addition, LT3 plays a role in specific clinical contexts such as preparation for radioactive iodine ablation in thyroid cancer and management of myxedema coma. This consensus aims to update recommendations for the optimal management of patients with hypothyroidism who experience suboptimal outcomes with LT4 monotherapy and may benefit from LT3 therapy. The document, developed by experts from the Indian Thyroid Society through extensive review and deliberation, provides practical, evidence-based guidance to help clinicians achieve improved therapeutic outcomes and enhanced quality of life for their patients.