Triiodothyronine levels in athyreotic pediatric patients during levothyroxine therapy.

94% of athyreotic pediatric patients on LT4 monotherapy achieved T3 levels within the normal range post-total thyroidectomy.

• 102 of 108 patients demonstrated T3 levels in the normal range post-TT.
• The cohort included 108 patients on either LT4 replacement (n=53) or LT4 suppression (n=55) therapy.
• Patients were under 19 years old and underwent total thyroidectomy between 2010-2021.
• LT4 replacement was used for Graves' disease patients targeting TSH normalization; LT4 suppression was used for differentiated thyroid cancer patients targeting TSH suppression.

The majority of pediatric patients on LT4 replacement therapy had post-thyroidectomy T3 levels in the lower half of the normal range.

• 83% (44/53) of patients on LT4 replacement displayed post-TT T3 levels in the lower half of the normal range.
• 50% (22/44) of these patients with lower-half T3 levels had post-TT fT4 levels above the upper limit of the normal range.
• LT4 replacement therapy targeted TSH normalization in Graves' disease patients.

The majority of pediatric patients on LT4 suppression therapy had post-thyroidectomy T3 levels in the lower half of the normal range.

• 56% (31/55) of patients on LT4 suppression displayed post-TT T3 levels in the lower half of the normal range.
• 48% (15/31) of these patients with lower-half T3 levels had post-TT fT4 levels above the upper limit of the normal range.
• LT4 suppression therapy targeted TSH suppression in differentiated thyroid cancer patients.

A significant number of pediatric patients did not achieve similar T3 and T4:T3 levels pre- and post-total thyroidectomy on LT4 monotherapy.

• Pre- and post-surgical TSH, T3, and T4 levels were compared retrospectively.
• The altered T4:T3 ratios occurred despite many patients having fT4 levels above the upper limit of normal, suggesting peripheral conversion of T4 to T3 was insufficient.
• This pattern was observed across both replacement and suppression therapy groups.

In adults post-total thyroidectomy on LT4 monotherapy, approximately 15% have altered T4:T3 ratios, and the clinical impact on health-related quality of life remains debated.

• This adult figure of approximately 15% is cited as background context for the pediatric study.
• Ongoing debate exists regarding the clinical impact of altered T4:T3 ratios with respect to health-related quality of life (hrQOL) in adults.
• The ability to normalize T3 and T4 levels on LT4 monotherapy for pediatric patients post-TT had not been previously described prior to this study.

The authors concluded that future multi-center prospective studies are warranted to evaluate LT4 monotherapy compared to combined LT4/LT3 therapy in athyreotic pediatric patients.

• The rationale is to determine the potential clinical impact of altered T3 levels in this population.
• The current study was retrospective and single-center, limiting generalizability.
• LT4 monotherapy is the current recommended approach for treating pediatric patients post-total thyroidectomy based on the assumption that peripheral T4 to T3 conversion normalizes thyroid hormone levels.