Objective: To examine the prevalence of T3 toxicosis in Thai ambulatory patients with thyrotoxicosis.

Materials and Methods: The present cross-sectional retrospective study in newly diagnosed thyrotoxicosis patients was performed at the outpatient department of Siriraj Hospital (Bangkok, Thailand) between January 2009 and December 2013. Recorded data included age, gender, current residence, duration of symptoms, etiology, and results of thyroid function tests. Patients were categorized into the T3, T4, or T3 and T4 toxicosis groups.

Results: Three hundred fourteen thyrotoxicosis patients were included. The mean age was 44.1 years, and 69% were female. The causes of thyrotoxicosis were Graves’ disease (93.3%), toxic adenoma/toxic multinodular goiter (2.9%), and subacute/painless thyroiditis (3.8%). The prevalence of T3 toxicosis and T4 toxicosis was 3.5% and 10.8%, respectively. The majority of patients with T3 toxicosis were male and residing outside Bangkok. The T3 toxicosis group had significantly lower level of total T3 compared with the T3 and T4 toxicosis group.

Conclusion: The 3.5% prevalence of T3 toxicosis observed in the present study suggests free T4 and thyroid stimulating hormone as the recommended initial laboratory investigations in Thai patients with suspected thyrotoxicosis.

Keywords: Prevalence, T3 toxicosis, Ambulatory Thai patients, Thyrotoxicosis