چکیده (انگلیسی):

Background: The measurement of free thyroid hormone, instead of the total form, is more commonly
used in current practice. We aimed to evaluate the usefulness of the ratio of serum free triiodothyronine
(FT3, pg/mL) to free thyroxine (FT4, ng/dL) for differentiating Graves' disease from subacute thyroiditis.
Materials and methods: Medical records of thyrotoxic patients aged >15 years who had measurement of
FT3, FT4 and thyrotropin on the first diagnosis of thyrotoxicosis before initiating treatment were
retrospectively reviewed. Data were collected from all clinics, and were not limited to the endocrine
clinic. Pregnant women were excluded.
Results: A total of 548 patients (468 with Graves' disease, 40 with subacute thyroiditis and 40 with toxic
adenoma/multinodular goiter) were recruited. Mean age was 43.9 ± 15.4 years. Most were female 434
(79.2%), and goiter was present in 55.3%. Prevalence of T3-toxicosis and T4-toxicosis were 5.6% and 6.6%,
respectively. Mean FT3/FT4 ratios were 4.62 ± 2 (102 pg/ng) in patients with Graves' disease and
2.73 ± 0.5 in subacute thyroiditis. The area under the ROC curve of the FT3/FT4 ratio for diagnosis of
Graves' disease was 0.83 (95%CI, 0.76e0.91). Cutoff level of this ratio >4.4 offered sensitivity of 47.2% and
specificity of 92.8%.
Conclusions: FT3/FT4 ratio of >4.4 (102 pg/ng) may help in differentiating the cause of thyrotoxicosis.