Highlights
The FT3/FT4 ratio appears to be a clinically useful marker of relapse risk in pediatric autoimmune hyperthyroidism, both at diagnosis and before antithyroid drug withdrawal.
In this retrospective cohort, half of the children who stopped antithyroid drugs relapsed, and most relapses occurred within 12 months.
An FT3/FT4 ratio of at least 0.42 at diagnosis showed good sensitivity for relapse prediction and remained an independent predictor in multivariable analysis, alongside orbitopathy.
The finding is promising, but it needs prospective validation before it can be used as a stand-alone decision tool for treatment duration.
Background
Pediatric autoimmune hyperthyroidism, most commonly Graves disease, is a chronic autoimmune condition that can be difficult to manage because remission after antithyroid drug (ATD) therapy is uncertain. Clinicians must often decide when it is safe to withdraw medication, yet stopping too early exposes the child to relapse, while prolonged treatment may increase the burden of adverse effects, adherence problems, and family anxiety.
Traditional predictors of relapse include younger age, larger goiter, higher thyroid-stimulating hormone receptor antibody levels, more severe biochemical hyperthyroidism, and orbitopathy. However, these markers do not fully solve the clinical dilemma. The FT3/FT4 ratio has gained attention as a potentially simple marker of disease activity and thyroid hormone economy. Because Graves disease often drives relatively greater triiodothyronine (T3) production than thyroxine (T4), a higher FT3/FT4 ratio may reflect more active disease or a thyroid gland that remains more autonomous and harder to suppress.
This study by Abbate and colleagues asked a practical question: can the FT3/FT4 ratio help predict which pediatric patients will relapse after stopping ATD therapy?
Study Design
This was a retrospective cohort study that included 80 patients with autoimmune hyperthyroidism diagnosed between 2000 and 2021. Clinical and biochemical data were collected at diagnosis and during follow-up. Among these patients, 48 discontinued antithyroid therapy and were therefore evaluable for relapse after withdrawal.
The investigators compared patients who relapsed with those who remained in remission after ATD withdrawal. They used receiver operating characteristic (ROC) analysis to identify a potentially useful FT3/FT4 cutoff and logistic regression to determine whether the ratio retained predictive value after accounting for other factors. The primary clinical outcome was relapse after treatment withdrawal, with follow-up details indicating that most relapses occurred within 12 months.
Key Findings
Of the 48 patients who stopped ATD therapy, 24 relapsed, which corresponds to a relapse rate of 50%. Importantly, relapse was common and occurred predominantly within the first year after withdrawal. This timing is clinically relevant because it reinforces the need for close biochemical monitoring after medication discontinuation, especially in the early months.
The FT3/FT4 ratio distinguished relapsers from non-relapsers at two time points. At diagnosis, the median FT3/FT4 ratio was 0.46 in patients who later relapsed versus 0.36 in those who did not, a statistically significant difference. At the time of ATD withdrawal, the gap persisted: 0.43 versus 0.33, again favoring higher ratios in the relapse group. The consistency of this association across both baseline disease presentation and later treatment decision point strengthens the argument that the ratio reflects underlying disease biology rather than a transient laboratory fluctuation.
ROC analysis suggested that an FT3/FT4 ratio of 0.42 or higher at diagnosis could be used as a risk threshold. At that cutoff, sensitivity was 83% and specificity was 66% for predicting relapse. In practical terms, this means the test would correctly identify most children who later relapse, while also misclassifying a substantial minority of those who would go on to remain in remission. That performance profile is useful for a screening-style risk marker, but it is not strong enough to replace established clinical judgment.
Multivariable analysis is especially important because relapse risk is multifactorial. In that analysis, an FT3/FT4 ratio of at least 0.42 at diagnosis remained independently associated with relapse, with an odds ratio of 7.18 and a p value of 0.012. Orbitopathy was also an independent predictor. These two findings suggest that the biochemical signature of T3-predominant hyperthyroidism and the presence of extrathyroidal autoimmune activity together identify a subgroup at higher risk of disease persistence or recurrence.
In univariate analyses, longer time to FT3 normalization was associated with relapse, as was orbitopathy. This is clinically intuitive: slower biochemical response may reflect more active disease or incomplete suppression on therapy, and orbitopathy may indicate a more robust autoimmune phenotype. However, because these were not all retained as independent predictors in multivariable testing, they should be interpreted as supportive rather than definitive markers.
One particularly useful feature of the study is the evaluation of the FT3/FT4 ratio both at diagnosis and before withdrawal. A marker that remains elevated when treatment is being tapered or stopped may be more actionable for clinicians than a single baseline value. The study suggests that persistent T3 predominance at the end of therapy may be a warning sign that remission is less secure.
Expert Commentary
Why might the FT3/FT4 ratio matter biologically? In Graves disease, the stimulating antibodies that drive thyroid hormone production may lead to disproportionate T3 secretion. T3 predominance has long been recognized in more active or severe hyperthyroidism, and the FT3/FT4 ratio can be viewed as a compact summary of that pattern. If the ratio remains high even after months of ATD therapy, it may indicate ongoing autoimmune stimulation that has not fully quieted.
The study’s strengths include its clinically meaningful question, long observation window, and focus on a pediatric population in which decisions about ATD withdrawal are especially difficult. The use of both ROC analysis and multivariable regression adds methodological value, and the finding that relapse occurred mostly within 12 months matches real-world clinical experience.
That said, several limitations deserve emphasis. First, the retrospective design limits causal inference and leaves room for confounding. Second, only 48 patients stopped therapy, so the effective sample for the main outcome was modest. Third, the study spans two decades, during which diagnostic assays, treatment practices, and follow-up strategies may have changed. Fourth, the abstract does not specify whether thyroid-stimulating hormone receptor antibody levels, goiter size, medication adherence, or ATD dosing patterns were consistently incorporated into the models, all of which could influence relapse risk.
Generalizability is another issue. This was a pediatric cohort from a single clinical context, and performance of the 0.42 cutoff may differ in other populations, assay platforms, or treatment settings. The exact FT3/FT4 threshold is therefore best viewed as hypothesis-generating rather than universal.
Still, the result is clinically attractive because the FT3/FT4 ratio is easy to obtain from routine thyroid function testing. If validated prospectively, it could help endocrinologists refine withdrawal decisions, identify children who need longer treatment, and target closer follow-up after stopping ATDs. It may be most useful when combined with established predictors such as orbitopathy, antibody status, age at diagnosis, and duration of biochemical normalization.
Clinical Implications
For practicing clinicians, the study suggests a simple risk-stratification approach: a child with Graves disease who has persistent T3 predominance, especially an FT3/FT4 ratio of 0.42 or higher, may warrant more caution before ATD withdrawal. If orbitopathy is also present, the risk signal is stronger.
In practical terms, this could influence three decisions. First, clinicians may choose to continue ATD therapy longer before attempting withdrawal. Second, they may intensify counseling about relapse risk and the need for post-withdrawal monitoring. Third, they may have a lower threshold to check thyroid function earlier and more frequently during the first year after discontinuation.
It is important not to overstate the result. The FT3/FT4 ratio should not replace antibody testing, clinical assessment, or family-centered shared decision-making. Rather, it may add a useful layer of information when the decision to stop therapy is otherwise uncertain.
Conclusion
This study provides evidence that the FT3/FT4 ratio is associated with relapse after ATD withdrawal in pediatric autoimmune hyperthyroidism. A ratio of at least 0.42 at diagnosis was independently predictive of relapse, and higher ratios were also seen before withdrawal in children who later recurred. Together with orbitopathy, the FT3/FT4 ratio may help identify children at higher risk of disease persistence.
The key message is pragmatic: a routine thyroid hormone ratio may offer additional prognostic information at a point in care where decisions are often difficult. Before it can be incorporated into guidelines or used as a standard withdrawal criterion, however, the finding should be confirmed in larger, prospective, multi-center cohorts with standardized follow-up.
Funding and ClinicalTrials.gov
The abstract does not report funding details or a ClinicalTrials.gov registration number.
References
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5. Abbate M, Vincenzi G, Mora S, Tarantola G, Petralia IT, Santagiuliana C, Del Giacco L, Zanelli S, Vigone MC. The FT3/FT4 Ratio Predicts Relapse After Antithyroid Drug Withdrawal in Pediatric Autoimmune Hyperthyroidism. J Clin Endocrinol Metab. 2026. PMID: 41913979.