Journal List > Endocrinol Metab > v.27(2) > 1085939

Lee, Kim, Hahm, Jung, Kim, Kim, Chung, Choi, and Jung: Differential Diagnostic Value of Total T3/Free T4 Ratio in Graves' Disease and Painless Thyroiditis Presenting Thyrotoxicosis

Abstract

Background

It is important to differentiate Graves' disease from that of painless thyroiditis in patients with thyrotoxicosis. In this study, we evaluated the usefulness of total T3 to free T4 ratio in making a differential diagnosis between Graves' disease and painless thyroiditis.

Methods

We reviewed medical records of thyrotoxic patients, who had been diagnosed with Graves' disease or painless thyroiditis, from October 2009 to July 2011. We assessed clinical characteristics, serum levels of total T3, free T4, thyroid stimulating hormone, thyrotropin-binding inhibitory immunoglobulin, and findings of 99mTechnetium thyroid scan. We analyzed the total T3/free T4 ratios between Graves' disease and painless thyroiditis patients.

Results

A total of 76 untreated thyrotoxic patients "49 Graves' disease and 27 painless thyroiditis" were examined. The total T3, free T4 levels and the total T3/free T4 ratios were significantly higher in patients with Graves' disease than in those with painless thyroiditis (P < 0.001). In the total T3/free T4 ratio > 73, the possibility of Graves' disease was significantly higher than in painless thyroiditis (sensitivity, 75.5%; specificity, 70.3%). The sensitivity and specificity of the total T3/free T4 ratio in patients with free T4 < 3.6 ng/dL have been increased (sensitivity, 100%; specificity, 71.4%).

Conclusion

The total T3/free T4 ratios was useful for making a differential diagnosis between Graves' disease and painless thyroiditis.

Figures and Tables

Fig. 1
Individual serum total T3/free T4 ratios in Graves' disease and painless thyroiditis. Total T3/free T4 ratio in patients with Graves' disease was significantly (P < 0.001) higher than that in patients with painless thyroiditis.
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Fig. 2
Relationship between total T3/free T4 ratio and free T4 value in patients with Graves' disease and painless thyroiditis. Upper-left areas above the line represent the total T3/free T4 ratio of > 73. The ratios in the Graves' disease groups increased as the free T4 values decreased.
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Fig. 3
Individual serum total T3/free T4 ratios of free T4 < 3.6 ng/dL group and free T4 > 3.6 ng/dL group with Graves' disease and painless thyroiditis. The total T3/free T4 ratios were significantly higher in free T4 < 3.6 ng/dL group with Graves' disease. Upper areas above the line represent the total T3/free T4 ratio of > 73.
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Table 1
Baseline characterisitics in patients with Graves' disease and painless thryoiditis
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Values are expressed as mean ± SD. A P value < 0.05 was considered significant.

Table 2
Differential cut-off points of Graves' disease from painless thyroiditis
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AUC, area under the curves.

Table 3
Differentiation of Graves' disease from painless thyroiditis according to the free T4 levels
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AUC, area under the curves; GD, Graves' disease; PT, painless thyroiditis.

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