Residual Hypothyroid Symptoms Despite Normal TSH: Association with Free T3
Keywords:
Free Triiodothyronine (fT3), Hypothyroidism, Levothyroxine Therapy, Residual symptoms, Thyroid-Stimulating Hormone (TSH)Abstract
Abstract
Background: Most hypothyroid patients on levothyroxine (LT4) achieve normal TSH levels, yet some experience persistent symptoms despite biochemical euthyroidism.
Objective: To investigate the relationship between residual hypothyroid symptoms, TSH levels within normal range, and free triiodothyronine (fT3) in LT4-treated patients.
Methods: Retrospective case series of primary hypothyroidism patients on stable LT4 with normal-range TSH but persistent symptoms. Patients were stratified by low-normal versus high-normal TSH. Symptom severity was assessed via questionnaire and compared with TSH, free T4, and fT3 levels.
Results: Patients with low-normal TSH had fewer symptoms and significantly higher fT3 levels than those with high-normal TSH. Symptomatic patients had lower fT3 than asymptomatic patients (2.87 vs. 3.21 pg/mL, p<0.001). Logistic regression showed low-normal TSH and elevated fT3 predicted symptom resolution.
Conclusion: Persistent hypothyroid symptoms in LT4-treated patients may result from relatively lower fT3 and high-normal TSH levels. Targeting low-normal TSH with fT3 monitoring may improve outcomes. Large-scale prospective studies are needed to confirm these findings and optimize treatment strategies.
