Abstract
Background The results of previous studies on the usefulness of free triiodothyronine (FT3) to free thyroxine (FT4) are controversial. We investigated the usefulness of FT3, FT4, and FT3/FT4 ratio in differentiating Graves' disease (GD) from destructive thyroiditis. Methods A total of 126 patients with untreated GD, 36 with painless thyroiditis, 18 with painful subacute thyroiditis, and 63 healthy controls, were recruited. The levels of FT3 and FT4 and the FT3/FT4 ratios for the different etiologies of thyrotoxicosis were evaluated separately by receiver operating characteristic (ROC) curve analysis. The expression levels of type 1 and type 2 deiodinase (DIO1 and DIO2) in thyroid tissues were also investigated. Results The optimal cut-off values were 7.215 pmol/L for FT3, 21.71 pmol/L for FT4, and 0.4056 for the FT3/FT4 ratio. The specificity and positive predictive value of the FT3/FT4 ratio were highest for values > 0.4056. DIO1 mRNA expression was significantly higher in the thyroid tissue of patients with GD (P = 0.013). Conclusions We demonstrated that the FT3/FT4 ratio was useful in differentiating GD from destructive thyroiditis. In addition, a relatively high expression of type 1 deiodinase in the thyroid might be responsible for the high FT3/FT4 ratio in patients with GD.
Highlights
Thyrotoxicosis can occur if thyroid hormone is passively released in excessive amounts or if the thyroid follicle cells are constitutively activated for thyroid hormone synthesis and secretion
We recruited 126 untreated Graves’ disease (GD) patients (40.25 ± 12.49 years), 92.8% (117/126) of whom were TRAb positive. 7.2% (9/126) of patients who were TRAb-negative were confirmed to have GD based on a typical “thyroid storm pattern” in ultrasound imaging of the neck and diffuse increase in radioactive iodine (RAI) uptake
The results showed that the T3/T4 ratio was higher in patients with GD than those in patients with subacute thyroiditis and painless thyroiditis, with proposed T3/T4 ratios of >20 for GD and toxic nodular goiter and
Summary
Thyrotoxicosis can occur if thyroid hormone is passively released in excessive amounts or if the thyroid follicle cells are constitutively activated for thyroid hormone synthesis and secretion. Due to thyroid follicle cell breakdown from an autoimmune reaction, infection, drugs, painless thyroiditis, and subacute thyroiditis, known as destructive thyroiditis, are less common causes of thyrotoxicosis. The clinical diagnosis of patients with thyrotoxicosis is generally based on the physical manifestations and laboratory test results. It is difficult to differentiate GD from painless thyroiditis based on the physical manifestations. The radioactive iodine (RAI) uptake test is a useful method to differentiate thyrotoxicosis etiologies; it is contradicted in specific situations such as in pregnant or lactating women. We investigated the usefulness of FT3, FT4, and FT3/FT4 ratio in differentiating Graves’ disease (GD) from destructive thyroiditis. We demonstrated that the FT3/FT4 ratio was useful in differentiating GD from destructive thyroiditis. A relatively high expression of type 1 deiodinase in the thyroid might be responsible for the high FT3/FT4 ratio in patients with GD
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