Comparison of triiodothyronine level in patients treated with levothyroxine for different causes of hypothyroidism

Abstract

Objective: Several lines of evidence suggest that the symptoms of hypothyroidism, including psychological symptoms and metabolic effects, persist in a significant percentage of patients treated with levothyroxine (L-T4). A hypothesis to explain this phenomenon is that the triiodothyronine (L-T3) serum levels may not be completely normalized. This study aimed to com-pare the level of serum free T3 (FT3) in patients who are biochemically euthyroid after L-T4 monotherapy with different underlying causes of hypothyroidism. Material and Methods: This cross-sectional study was conducted on patients with hypothyroidism who received L-T4 monotherapy and were bioc-hemically euthyroid. The serum levels of thyroid-stimulating hormone (TSH), free T4 (FT4), FT3, and FT3/FT4 ratio were measured in these patients. Patients were divided into three groups based on the cause of hypothyroidism (radioiodine the-rapy, thyroidectomy and Hashimoto), and the results of biochemical tests of the thyroid were compared in three groups. Results: Of the 78 patients studied, 12 (15.4%) cases were male, and 66 (84.6%) cases were female. Among the variables studied, only the mean value of FT3 was significantly different in the three groups (p=0.006), where the highest mean value was seen in the Hashimoto group, and the lowest mean value was seen in the radioiodine therapy group. Conclusion: The results of this study showed that although hypothyroidism patients can be optimally treated with L-T4 alone, in many of these patients, the level of FT3 will not be in therapeutic range, and the mean serum FT3 levels in these patients could be related to their hypothyroidism causes.