Utility of the FT3-to-FT4 ratio as a screening marker for pediatric Graves' disease

Graves' disease (GD) is the most common cause of pediatric thyrotoxicosis; however, differentiating it from other conditions is challenging. A high free triiodothyronine-to-free thyroxine ratio (FT3/FT4) ratio has been established as an indicator of GD in adults. In this retrospective observational study, we aimed to investigate the utility of the FT3/FT4 ratio as a screening marker for pediatric GD by analyzing the medical records of 105 patients aged 1-18 years who presented with thyrotoxicosis at three hospitals in Japan. The participants were divided into a GD group (TSH receptor antibody > 2.0 IU/L and requiring antithyroid drug for at least six months; n = 70) and a non-GD group (n = 35). The median (range) of the FT3/FT4 ratio was significantly higher in the GD group than in the non-GD group (3.41 [1.90-5.22] vs. 2.92 [1.50-4.40]; p < 0.05). Receiver operating characteristic curve analysis of the FT3/FT4 ratio revealed an area under the curve of 0.693 (95% confidence interval [CI], 0.577-0.808). At the optimal cutoff value of 2.88, the FT3/FT4 ratio demonstrated a sensitivity of 0.86 (95% CI: 0.80-0.91) and a specificity of 0.51 (95% CI: 0.39-0.62) for GD screening. These findings suggest the usefulness of the FT3/FT4 ratio as a screening marker for pediatric GD.