Basal Serum Thyroxine Level should Guide Initial Thyroxine Replacement Dose in Neonates with Congenital...

Area of Science:

• Pediatric Endocrinology
• Thyroid Disorders
• Pharmacology

Background:

• Congenital hypothyroidism (CH) requires thyroid hormone replacement therapy.
• Current guidelines recommend high-dose sodium levothyroxine (Na-LT4) initiation (10-15 μg/kg/day).
• High initial doses of Na-LT4 may lead to iatrogenic hyperthyroidism.

Purpose of the Study:

• To evaluate the impact of varying initial Na-LT4 doses on serum thyroid hormone levels in CH patients.
• To determine if initial Na-LT4 dosage can be tailored based on CH severity.
• To assess the incidence of hyperthyroxinemia with different initial treatment regimens.

Main Methods:

• Retrospective analysis of 52 patients with primary CH.
• Classification of CH severity into mild, moderate, and severe based on initial free thyroxine (fT4) levels.
• Comparison of time to achieve target hormone levels and incidence of hyperthyroxinemia across severity groups.

Main Results:

• Initial mean Na-LT4 doses varied by severity: 6.9±3.3 μg/kg/day (mild), 9.4±2.2 μg/kg/day (moderate), and 10.2±2 μg/kg/day (severe).
• Time to reach target fT4 levels did not significantly differ by CH severity (p=0.478).
• Hyperthyroxinemia (fT4 >1.94 ng/dL) occurred in 25.9% (mild), 72.7% (moderate), and 57.1% (severe) of patients (p=0.016).

Conclusions:

• Not all CH patients necessitate high initial Na-LT4 doses; dosage may be guided by baseline thyroid hormone levels.
• Moderate and severe CH patients experienced iatrogenic hyperthyroxinemia even with doses near the lower recommended range.
• Lower initial Na-LT4 doses with closer early follow-up may be a safer approach for CH management.