Association Between FT4/FT3 Ratio and Short-Term Treatment Response in Differentiated Thyroid Cancer Patients.

Background: Thyroid cancer is the most common endocrine tumor, with its incidence increasing worldwide. Although differentiated thyroid cancer (DTC) generally has a good prognosis, some patients still experience recurrence or persistent lesions after initial treatment. This study aimed to explore the relationship between free thyroxine (FT4)/free triiodothyronine (FT3) ratio and short-term treatment response in patients with DTC. Methods: A retrospective analysis was conducted on 225 patients with DTC who received treatment at the Nuclear Medicine Department of Deyang People's Hospital from 2019 to 2022. All patients underwent total or subtotal thyroidectomy followed by radioactive iodine therapy. Clinical data and preoperative laboratory test results were collected, and multivariable logistic regression analysis was used to evaluate the association between the FT4/FT3 ratio and the short-term treatment response in DTC, as well as trend analysis and restricted cubic spline (RCS) evaluation for nonlinear relationships. Results: Among the 225 patients, 159 (70.7%) achieved an excellent response (ER). Compared to the non-ER group, the ER group had higher levels of FT4 (p = 0.040). After multivariate adjustment, the FT4/FT3 ratio was significantly associated with DTC prognosis (OR = 0.40, 95% CI: 0.22-0.68). Trend analysis showed that patients in the highest quartile of FT4/FT3 ratio were more likely to achieve ER status (OR = 0.20, 95% CI: 0.07-0.55; P for trend = 0.006). RCS analysis indicated a dose-response relationship between FT4/FT3 ratio and short-term prognosis of DTC (P for overall = 0.006; P for nonlinear = 0.887). Conclusion: The FT4/FT3 ratio is significantly associated with short-term treatment response in patients with DTC. A higher FT4/FT3 ratio may be an independent predictive factor for a favorable prognosis in DTC patients. Future studies should further investigate its mechanisms and potential clinical applications.