The Free T3/Free T4 Ratio Predicts Relapse After Antithyroid Drug Withdrawal in Pediatric Autoimmune Hyperthyroidism

The likelihood of remission in patients with autoimmune hyperthyroidism (AH) depends on several prognostic factors. The free T3 (FT3)/free T4 (FT4) ratio has been suggested as a potential marker of disease severity and prognosis.

To evaluate the prognostic value of the FT3/FT4 ratio in predicting the likelihood of relapse in patients with AH.

This retrospective cohort study included 80 patients with AH diagnosed between 2000 and 2021. Clinical and biochemical data were collected at diagnosis and during follow-up to assess the likelihood of remission in patients attempting to discontinue antithyroid drug (ATD) therapy. Receiver operating characteristic analysis and logistic regression were used to identify predictors of relapse.

Of the 48 patients who discontinued ATD therapy, 24 (50%) relapsed, predominantly within 12 months. The FT3/FT4 ratio was significantly higher in patients who relapsed both at diagnosis (median 0.46 vs 0.36; P .001) and at ATD withdrawal (median 0.43 vs 0.33; P < .001). An FT3/FT4 ratio ≥0.42 at diagnosis predicted relapse with 83% sensitivity and 66% specificity. In a multivariate analysis, FT3/FT4 ratio ≥0.42 at diagnosis (odds ratio 7.18; P .012) and the presence of orbitopathy were identified as independent predictors of relapse. Longer time to FT3 normalization (P .02) and orbitopathy were associated with relapse in univariate analyses (P .039).

The FT3/FT4 ratio, measured both at diagnosis and before ATD withdrawal, is a significant predictor of relapse in AH. This parameter may represent a useful tool for guiding decisions about treatment duration and withdrawal.